Montana Food Products :: Research

Dietary Fiber: An Essential Part of a Healthy Diet

Eat more fiber. You've probably heard it before. But do you know why fiber is so good for your health? Dietary fiber — found mainly in fruits, vegetables, whole grains and legumes — is probably best known for its ability to prevent or relieve constipation. But fiber can provide other health benefits as well, such as lowering your risk of diabetes and heart disease.

+General Information

+What is Dietary Fiber

What is Dietary Fiber?

Dietary fiber — also known as roughage or bulk — is undoubtedly one of the most talked about nutrients for health promotion and disease prevention. In fact, dietary fiber is the focus of two FDA-approved health claims that appear on foods labels touting the benefits of high fiber foods for the prevention of heart disease and certain types of cancer.

Since the early 1950's, when the term "fiber" first began to be used in scientific journals, there has been considerable controversy among food scientists, nutritionists, and medical experts about the exact definition of dietary fiber. In fact, even the United States Food and Drug Administration, the federal agency responsible for overseeing food labeling, has no formal, written definition of dietary fiber. For food labeling purposes and the determination of health claims, the FDA has adopted the analytical methods that the Association of Official Analytical Chemists uses for defining dietary fiber.

Most experts agree that a key defining characteristic of dietary fiber is that it's derived from the edible parts of plants that are not broken down by human digestive enzymes. It is the indigestible portion of plant foods that move food through the digestive system, absorbing water and making defecation easier. Dietary fiber consists of non-starch polysaccharides such as cellulose and many other plant components such as dextrins, inulin, lignin, waxes, chitins, pectins, beta-glucans and oligosaccharides.

However, many people believe that this definition is too ambiguous and that a more clear, internationally-accepted definition is needed to ensure that the total fiber counts on food labels are consistent and accurate. In recent years there has been a movement among various organizations to include the physiological benefits of dietary fiber in a new definition. For example, the American Association of Cereal Chemists proposed a new definition of dietary fiber that includes the statement "Dietary fibers promote beneficial physiological effects including laxation and/or blood cholesterol attenuation and/or blood glucose attenuation."

In addition, the Institute of Medicine at the National Academy of Sciences (the organization responsible for issuing Recommended Dietary Allowances) has proposed a new definition that differentiates between dietary fiber and added fiber. According to this definition, dietary fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants.

Added fiber, which refers to fiber that is added to foods during food processing, consists of isolated nondigestible carbohydrates that have proven beneficial physiological effects in humans. For food labeling purposes, the Institute of Medicine defines Total Fiber as the sum of Dietary Fiber and Added Fiber.

Despite the controversy surrounding the exact definition of dietary fiber, experts agree on one important thing - dietary fiber is an important weapon in the fight against heart disease, colon cancer, diabetes, and obesity.

Categories of Dietary Fiber

· Cellulose, found in bran, legumes, peas, root vegetables, cabbage family, outer covering of seeds, and apples
· Hemicellulose, found in bran and whole grains
· Polyfructoses (Inulin and Oligofructans)

· Galactooligosaccharides

· Gums, found oatmeal, barley, and legumes.

· Mucilages

· Pectins, found in apples, strawberries, and citrus fruits

· Lignin, found in root vegetables, wheat, fruits with edible seeds (such as strawberries)

· Resistant Starches, found in ripe bananas, potatoes

· Fiber is often classified into two categories: that which doesn’t dissolve in water (insoluble fiber) and that which does (soluble fiber). Both types of fiber are present in all plant foods, with varying degrees of each according to a plant’s characteristics.

· Insoluble fiber. This type of fiber possesses passive water-attracting properties that help to increase bulk, soften stool and shorten transit time through the intestinal tract. It increases the movement of material through your digestive system, so it can be of benefit to those who struggle with constipation or irregular stools. Whole-wheat flour, wheat bran, nuts and many vegetables are good sources of insoluble fiber.
· Soluble fiber. This type of fiber undergoes metabolic processing via fermentation, yielding end-products with broad, significant health effects. Soluble fiber dissolves in water to form a gel-like material. It can help lower blood cholesterol and glucose levels. You can find generous quantities of soluble fiber in oats, peas, beans, apples, citrus fruits, carrots, barley and psyllium.

Courtesy of: The George Mateljan Foundation and the World's Healthiest Foods and The Mayo Clinic

+What is the function of Dietary Fiber?

What is the Function of Dietary Fiber?

Until very recently, the functions of a specific type of fiber were determined by whether or not the fiber was classified as soluble or insoluble. Soluble fibers, such as the type found in oat bran, are known to reduce blood cholesterol levels and normalize blood sugar levels.

On the other hand, insoluble fiber, such as the type found in wheat bran, are known to promote bowel regularity. Many commonly used plant sources of fiber contain both soluble and insoluble fibers. Psyllium husks, for example, contain a mixture of 70% soluble and 30% insoluble fibers. Despite the widespread use of the terms "soluble" and "insoluble" to describe the health benefits of dietary fiber, many medical and nutrition experts contend that these terms do not adequately describe the physiological effects of all the different types of fiber. These experts are now proposing the use of the terms "viscous" and "fermentability" in place of soluble and insoluble to describe the functions and health benefits of dietary fiber.

Reducing Cholesterol Levels

Like soluble fibers, viscous fibers lower serum cholesterol by reducing the absorption of dietary cholesterol. In addition, viscous fibers complex with bile acids, which are compounds manufactured by the liver from cholesterol that are necessary for the proper digestion of fat. After complexing with bile acids, the compounds are removed from circulation and do not make it back to the liver. As a result, the liver must use additional cholesterol to manufacture new bile acids. Bile acids are necessary for normal digestion of fat. Soluble fiber may also reduce the amount of cholesterol manufactured by the liver.

Normalizing Blood Sugar Levels

Viscous fibers also help normalize blood glucose levels by slowing the rate at which food leaves the stomach and by delaying the absorption of glucose following a meal. Viscous fibers also increase insulin sensitivity. As a result, high intake of viscous fibers plays a role in the prevention and treatment of type 2 diabetes. In addition, by slowing the rate at which food leaves the stomach, viscous fibers promote a sense of satiety, or fullness, after a meal, which helps to prevent overeating and weight gain.

Promoting Bowel Regularity

Certain types of fiber are referred to as fermentable fibers because they are fermented by the "friendly" bacteria that live in the large intestine. The fermentation of dietary fiber in the large intestine produces a short-chain fatty acid called butyric acid, which serves as the primary fuel for the cells of the large intestine and helps maintain the health and integrity of the colon.

Two other short-chain fatty acids produced during fermentation, propionic and acetic, are used as fuel by the cells of the liver and muscles. In addition, propionic acid may be responsible, at least in part, for the cholesterol-lowering properties of fiber. In animal studies, propionic acid has been shown to inhibit HMG-CoA reductase, an enzyme involved in the production of cholesterol by the liver. By lowering the activity of this enzyme, blood cholesterol levels may be lowered.

Fermentable fibers also help maintain healthy populations of friendly bacteria. In addition to producing necessary short-chain fatty acids, these bacteria play an important role in the immune system by preventing pathogenic (disease-causing) bacteria from surviving in the intestinal tract.

As is the case with insoluble fiber, fibers that are not fermentable in the large intestine help maintain bowel regularity by increasing the bulk of the feces and decreasing the transit time of fecal matter through the intestines. Bowel regularity is associated with a decreased risk for colon cancer and hemorrhoids (when the hemorrhoids are related to straining and constipation).

Summary of definition and potential health benefits In June 2007, the British Nutrition Foundation issued a statement to define dietary fiber more concisely and list the potential health benefits established to date:

“Dietary fiber has been used as a collective term for a complex mixture of substances with different chemical and physical properties which exert different types of physiological effects. The use of certain analytical methods to quantify dietary fiber by nature of its indigestibility results in many other indigestible components being isolated along with the carbohydrate components of dietary fiber. These components include resistant starches and oligosaccharides along with other substances that exist within the plant cell structure and contribute to the material that passes through the digestive tract. Such components are likely to have physiological effects. Yet, some differentiation has to be made between these indigestible plant components and other partially digested material, such as protein, that appears in the large bowel. Thus, it is better to classify fiber as a group of compounds with different physiological characteristics, rather than to be constrained by defining it chemically. Diets naturally high in fiber can be considered to bring about five main physiological consequences:

· improvements in gastrointestinal health
· improvements in glucose tolerance and the insulin response
· reduction of hyperlipidemia, hypertension and other coronary heart disease risk factors
· reduction in the risk of developing some cancers
· increased satiety and hence some degree of weight management

Therefore, it is not appropriate to state that fiber has a single all encompassing physiological property as these effects are dependent on the type of fiber in the diet. The beneficial effects of high fiber diets are the summation of the effects of the different types of fiber present in the diet and also other components of such diets. Defining fiber physiologically allows recognition of indigestible carbohydrates with structures and physiological properties similar to those of naturally occurring dietary fibers.”

Courtesy of the The Mayo Clinic

+Soluble (Fermentable) Fiber

Soluble / Fermentable Dietary Fiber

The American Association of Cereal Chemists defined soluble fiber this way: "the edible parts of plants or similar carbohydrates resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine."

There are several key words in that statement that invite analysis and comment for considering fermentable fiber.

· Edible parts of plants: indicates that all parts of a plant we eat — skin, pulp, seeds, stems, leaves, roots — contain fiber. Both insoluble and soluble sources are in those plant components.
· Carbohydrates: complex carbohydrates, such as long-chained sugars also called starch, oligosaccharides or polysaccharides, are excellent sources of fiber.
· Resistant to digestion and absorption in the human small intestine — foods providing nutrients are digested by gastric acid and digestive enzymes in the stomach and small intestine where the nutrients are released then absorbed through the intestinal wall for transport via the blood throughout the body. A food resistant to this process is undigested, as insoluble and soluble fibers are. They pass to the large intestine only affected by their absorption of water (insoluble fiber) or dissolution in water (soluble fiber).
· Complete or partial fermentation in the large intestine — the large intestine comprises a segment called the colon within which additional nutrient absorption occurs through the process of fermentation. Fermentation occurs by the action of colonic bacteria on the food mass, producing gases and short-chain fatty acids. It is these short-chain fatty acids — butyric, ethanoic (acetic), propionic, and valeric acids — that might have significant health properties.

Recognizing the growing scientific evidence for physiological benefits of increased fiber intake, regulatory agencies such as the US Food and Drug Administration (FDA) have given approvals to food products making health claims for fiber. In clinical trials to date, these fiber sources were shown to significantly reduce blood cholesterol levels, making them important to general cardiovascular health, and to lower risk of onset for some types of cancer.

Soluble (fermentable) fiber sources gaining FDA approval are:

· Psyllium seed husk (7 grams per day)

Beta-glucan from oat bran, whole oats, oatrim or rolled oats (3 grams per day)

Beta-glucan from whole grain or dry-milled barley (3 grams per day)

Other examples of fermentable fiber sources (from plant foods or biotechnology) used in functional foods and supplements include inulin, fructans, xanthan gum, cellulose, guar gum, fructooligosaccharides (FOS) and oligo- or polysaccharides.

Consistent intake of fermentable fiber through foods like berries and other fresh fruit, vegetables, whole grains, seeds and nuts is now known to reduce risk of some of the world’s most prevalent diseases — obesity, diabetes, high blood cholesterol, cardiovascular disease, and numerous gastrointestinal disorders including constipation, inflammatory bowel disease, ulcerative colitis, hemorrhoids, Crohn’s disease, diverticulitis, and colon cancer — all disorders of the intestinal tract where fermentable fiber can provide healthful benefits.

Insufficient fiber in the diet can complicate defecation. Low-fiber feces are dehydrated and hardened, making them difficult to evacuate — defining constipation and possibly leading to development of hemorrhoids.

Although many researchers believe that dietary fiber intake reduces risk of colon cancer, one study, conducted by researchers at the Harvard School of Medicine of over 88,000 women, did not show a statistically significant relationship between higher fiber consumption and lower rates of colorectal cancer or adenomas.

+Intake Guidelines

Guidelines on Dietary Fiber Intake

Fiber Consumption in the American Diet

On average, North Americans consume less than 50% of the dietary fiber levels required for good health. In the preferred food choices of today's youth, this value may be as low as 20%, a factor considered by experts as contributing to the obesity crisis seen in many developed countries.

How Much Fiber?

In 2002, the Food and Nutrition Board of the National Academy of Sciences Research Council issued Dietary Reference Intakes (DRI) for fiber (see Table 1). Previously, no national standardized recommendation existed. The new DRIs represent desirable intake levels established using the most recent scientific evidence available. The current recommendations range between 19 grams per day and 38 grams per day depending on age and gender. However, the average American only consumes 14 grams of dietary fiber per day.

Fiber Recommendations by Age and Gender

The Institute of Medicine and the Dietary Guidelines for Americans 2005 recommend that children (ages 1 and up) and adults consume 14 grams of fiber for every 1,000 calories of food they eat each day. This means a person who eats 2,500 calories each day should get at least 35 grams of fiber daily, while a person who eats 1,700 calories each day needs somewhat less fiber - about 24 grams. A toddler who eats only 1,300 calories each day needs about 18 grams of fiber.

Below are general fiber intake recommendations for different age groups and genders. These recommendations are based on the average daily calorie intake for people in these age and gender groups.

Table 1: Dietary Reference Intakes (DRI) for Fiber.
Age in Years	Grams/day Fiber	Average Calories/day
Children
1-3	19	1404
4-8	25	1789
Males
9-13	31	2265
14-18	38	2840
19-30	38	2818
31-50	38	2554
51-70	30	2162
70+	30	1821
Females
9-13	26	1910
14-18	26	1901
19-30	25	1791
31-50	25	1694
51-70	21	1536
70+	21	1381
Pregnancy
≤18	28	1404
18+	28	1404
Lactation
≤18	29	1404
18+	29	1404

For many people, meeting the DRI for fiber may require changes in their eating habits. Eating several servings of whole grains, fruits, vegetables and dried beans each day is good way to boost fiber intake. However, if you are not used to eating high fiber foods regularly, these changes should be made gradually to avoid problems with gas and diarrhea. Anyone with a chronic disease should consult a physician before greatly altering a diet.

What are deficiency symptoms for dietary fiber and what might contribute to a deficiency?

There is no identifiable, isolated deficiency disease caused by lack of fiber in the diet. However, research clearly indicates that low intake of dietary fiber (less than 20 grams per day) over the course of a lifetime is associated with development of numerous health problems including constipation, hemorrhoids, colon cancer, obesity and elevated cholesterol levels.

Even though fiber is often defined as the "undigestable" part of food, a certain amount of healthy digestive function is important for realizing the health benefits of this nutrient.

Inadequate chewing can prevent the health benefits of fiber from being realized, since fibers that cannot be solubilized (like lignins, celluloses, and some hemicelluloses) require extra chewing in order to participate in biochemical processes.

What are toxicity symptoms for dietary fiber?

Intake of dietary fiber in excess of 50 grams per day may cause an intestinal obstruction in susceptible individuals. In most individuals, however, this amount of fiber will improve (rather than compromise) bowel health.

Excessive intake of fiber can also cause a fluid imbalance, leading to dehydration. Individuals who decide to suddenly double or triple their fiber intake are often advised to double or triple their water intake for this reason.

In addition, excessive intake of nonfermentable fiber, typically in supplemental form, may lead to mineral deficiencies by reducing the absorption or increasing the excretion of minerals, especially when mineral intake is too low or when mineral needs are increased such as during pregnancy, lactation, or adolescence.

Reference

· Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. 2002. Washington, D.C.: The National Academies Press.
The Mayo Clinic

+Sources of Fiber

Sources of Dietary Fiber

Current recommendations from the United States National Academy of Sciences, Institute of Medicine, suggest that adults should consume 21-38 grams of dietary fiber per day, but the average American's daily intake of dietary fiber is only 12-18 grams. The American Dietetic Association recommends consuming a variety of fiber-rich foods.

Soluble fiber is found in varying quantities in all plant foods, including:

· Legumes (peas, soybeans, and other beans)
· Oats, rye, chia, and barley<
· Some fruits and fruit juices (particularly prune juice, plums and berries)
· Certain vegetables such as broccoli and carrots
· Root vegetables such as potatoes, sweet potatoes, and onions (skins of these vegetables are sources of insoluble fiber)
· Psyllium seed husk (a mucilage soluble fiber)

Legumes also typically contain shorter-chain carbohydrates indigestible by the human digestive tract but which may be metabolized by bacterial fermentation in the large intestine (colon), yielding short-chain fatty acids and gases (flatulence).

Sources of insoluble fiber include:

· Whole grain foods
· Bran
· Nuts and seeds<
· Vegetables such as green beans, cauliflower, zucchini, and celery
· Skins of some fruits, including tomatoes

The five most fiber-rich plant foods, according to the Micronutrient Center of the Linus Pauling Institute, are legumes (15-19 grams of fiber per US cup serving, including several types of beans, lentils and peas), wheat bran (17 grams per cup), prunes (12 grams), Asian pear (10 grams each) (3.6% by weight), and quinoa (9 grams).

Remarkable among plant foods, the Amazonian palmberry, açaí (Euterpe oleracea Mart.), has been analyzed by two research groups reporting its content of dietary fiber is 25-44% of total mass in freeze-dried powder. Rubus (bramble) fruits such as raspberry (8 grams of fiber per serving) and blackberry (7.4 grams of fiber per serving) are exceptional sources of fiber.

Dietary Fiber is affected by processing

Many whole foods contain 5 or more grams of fiber, and in their whole, unprocessed form, would be highly supportive of health. When foods are processed, however, most or all of this fiber is often lost.

For example, most breads sold nationally in the United States use a 60% extraction process in which 60% of the original wheat grain is kept in the flour, but 40% is discarded. The discarded part of the wheat includes the bran and the germ; these two components of the grain contain virtually all of its fiber.

As a result, 60% extraction wheat flour contains almost no fiber, even though the whole, unprocessed wheat grain contains an ample amount. Fruit juices and vegetable juices are also good examples of products which started out high-fiber in their whole, unprocessed state but ended up with virtually no fiber as a result of processing.

+World's Healthiest Foods

The World’s Healthiest Foods Nutrient Rating System Chart

The George Mateljan Foundation, a non-profit organization created to provide unbiased information on nutrition and diet, created the following chart as part of their Nutrient Rating System. The chart shows the foods which are an excellent, very good or good source of dietary fiber. Underneath the chart is a table that summarizes how the ratings were devised.

World's Healthiest Foods ranked as quality sources of: dietary fiber
Food	Serving Size	Cals	Amount (g)	DV (%)	Nutrient Density	Healthiest Foods Rating
Cinnamon, ground	2 tsp	11.8	2.48	9.9	15.1	very good
Turnip greens, cooked	1 cup	28.8	5.04	20.2	12.6	excellent
Basil, dried, ground	2 tsp	7.5	1.20	4.8	11.5	good
Coriander seeds	2 tsp	9.9	1.40	5.6	10.2	very good
Oregano, dried, ground	2 tsp	9.2	1.28	5.1	10.1	very good
Raspberries	1 cup	60.3	8.34	33.4	10.0	excellent
Thyme, dried, ground	2 tsp	7.9	1.08	4.3	9.8	good
Mustard greens, boiled	1 cup	21.0	2.80	11.2	9.6	excellent
Rosemary, dried	2 tsp	7.3	0.92	3.7	9.1	good
Romaine lettuce	2 cup	15.7	1.90	7.6	8.7	very good
Cauliflower, boiled	1 cup	28.5	3.35	13.4	8.5	excellent
Collard greens, boiled	1 cup	49.4	5.32	21.3	7.8	excellent
Broccoli, steamed	1 cup	43.7	4.68	18.7	7.7	excellent
Cloves, dried, ground	2 tsp	14.2	1.52	6.1	7.7	very good
Celery, raw	1 cup	19.2	2.04	8.2	7.7	very good
Swiss chard, boiled	1 cup	35.0	3.68	14.7	7.6	excellent
Cabbage, shredded, boiled	1 cup	33.0	3.45	13.8	7.5	very good
Spinach, boiled	1 cup	41.4	4.32	17.3	7.5	very good
Chili pepper, dried	2 tsp	25.5	2.64	10.6	7.5	very good
Black pepper	2 tsp	10.9	1.12	4.5	7.4	good
Fennel, raw, sliced	1 cup	27.0	2.70	10.8	7.2	very good
Green beans, boiled	1 cup	43.8	4.00	16.0	6.6	very good
Eggplant, cooked, cubes	1 cup	27.7	2.48	9.9	6.4	very good
Cayenne pepper, dried	2 tsp	11.2	0.96	3.8	6.2	good
Cranberries	0.50 cup	23.3	1.99	8.0	6.2	very good
Strawberries	1 cup	43.2	3.31	13.2	5.5	very good
Bell peppers, red, raw, slices	1 cup	24.8	1.84	7.4	5.3	very good
Winter squash, baked, cubes	1 cup	80.0	5.74	23.0	5.2	very good
Kale, boiled	1 cup	36.4	2.60	10.4	5.1	very good
Split peas, cooked	1 cup	231.3	16.27	65.1	5.1	very good
Summer squash, cooked, slices	1 cup	36.0	2.52	10.1	5.0	very good
Carrots, raw	1 cup	52.5	3.66	14.6	5.0	very good
Lentils, cooked	1 cup	229.7	15.64	62.6	4.9	very good
Brussel sprouts, boiled	1 cup	60.8	4.06	16.2	4.8	very good
Asparagus, boiled	1 cup	43.2	2.88	11.5	4.8	very good
Black beans, cooked	1 cup	227.0	14.96	59.8	4.7	very good
Green peas, boiled	1 cup	134.4	8.80	35.2	4.7	very good
Pinto beans, cooked	1 cup	234.3	14.71	58.8	4.5	very good
Cucumbers, slices, with peel	1 cup	13.5	0.83	3.3	4.4	good
Lima beans, cooked	1 cup	216.2	13.16	52.6	4.4	very good
Turmeric, powder	2 tsp	16.0	0.96	3.8	4.3	good
Flaxseeds	2 tbs	95.3	5.41	21.6	4.1	very good
Kiwifruit	1 each	46.4	2.58	10.3	4.0	very good
Wheat, bulgur, cooked	1 cup	151.1	8.19	32.8	3.9	very good
Tomato, ripe	1 cup	37.8	1.98	7.9	3.8	very good
Oranges	1 each	61.6	3.13	12.5	3.7	very good
Kidney beans, cooked	1 cup	224.8	11.33	45.3	3.6	very good
Barley, cooked	1 cup	270.0	13.60	54.4	3.6	very good
Apricots	1 each	16.8	0.84	3.4	3.6	good
Blueberries	1 cup	81.2	3.92	15.7	3.5	very good
Onions, raw	1 cup	60.8	2.88	11.5	3.4	very good
Garbonzo beans (chickpeas), cooked	1 cup	269.0	12.46	49.8	3.3	good
Papaya	1 each	118.6	5.47	21.9	3.3	good
Apples	1 each	81.4	3.73	14.9	3.3	good
Grapefruit	0.50 ea	36.9	1.69	6.8	3.3	good
Beets, Boiled	1 cup	74.8	3.40	13.6	3.3	good
Navy beans, cooked	1 cup	258.4	11.65	46.6	3.2	good
Figs, fresh	8 oz-wt	167.8	7.48	29.9	3.2	good
Rye, whole grain, uncooked	0.33 cup	188.7	8.22	32.9	3.1	good
Pear	1 each	97.9	3.98	15.9	2.9	good
Soybeans, cooked	1 cup	297.6	10.32	41.3	2.5	good
Yam (Dioscorea species), cubed, cooked	1 cup	157.8	5.30	21.2	2.4	good
Sweet potato, baked, with skin	1 each	95.4	3.14	12.6	2.4	good
Avocado, slices	1 cup	235.1	7.30	29.2	2.2	good
Mustard seeds	2 tsp	35.0	1.08	4.3	2.2	good
Prunes	0.25 cup	101.6	3.02	12.1	2.1	good
Buckwheat, cooked	1 cup	154.6	4.54	18.2	2.1	good
Shiitake mushrooms, raw	8 oz-wt	87.2	2.49	10.0	2.1	good
Olives	1 cup	154.6	4.30	17.2	2.0	good
Oats, whole grain, cooked	1 cup	145.1	3.98	15.9	2.0	good
Plum	1 each	36.3	0.99	4.0	2.0	good
Crimini mushrooms, raw	5 oz-wt	31.2	0.85	3.4	2.0	good
Miso	1 oz	70.8	1.86	7.4	1.9	good
Banana	1 each	108.6	2.83	11.3	1.9	good
Corn, yellow, cooked	1 cup	177.1	4.60	18.4	1.9	good
Pineapple	1 cup	76.0	1.86	7.4	1.8	good
Cantaloupe, cubes	1 cup	56.0	1.28	5.1	1.6	good
Potato, baked, with skin	1 cup	133.0	2.93	11.7	1.6	good
Sesame seeds	0.25 cup	206.3	4.24	17.0	1.5	good

World's Healthiest Foods Rating	Rule
excellent	DV>=75%	OR	Density>=7.6	AND	DV>=10%
very good	DV>=50%	OR	Density>=3.4	AND	DV>=5%
good	DV>=25%	OR	Density>=1.5	AND	DV>=2.5%

+Health Benefits of Dietary Fiber

+Obesity

Whole-grain consumption, dietary fibre intake and body mass index in the Netherlands cohort study
van de Vijver LP, van den Bosch LM, van den Brandt PA, Goldbohm RA. Eur J Clin Nutr. 2007 Sep 26

OBJECTIVES: To assess the association of whole-grain and (cereal) fibre intake with body mass index (BMI) and with the risk of being overweight (BMI>/=25) or obese (BMI>/=30 kg m(-2)).

SUBJECTS: A total of 2078 men and 2159 women, aged 55-69 years, were included in the analysis, after exclusion of subjects with diagnosed cancer or deceased within 1 year after baseline or with missing dietary information.

RESULTS: We found an inverse association between whole-grain consumption and BMI and risk of overweight and obesity in men as well as women. The association in men was stronger than in women; the risk of being obese as compared to normal weight was 10% (95% CI: 2-16%) and 4% (95% CI: 1-7%) lower for each additional gram of (dry) grain consumption in men and women, respectively. Fibre and cereal fibre intake were inversely associated with BMI in men only. Associations were similar after exclusion of likely under- and overreporters of energy. A retrospective analysis of baseline fibre intake and weight gain after the age of 20 years also showed a slight inverse association.

CONCLUSIONS: Whole-grain consumption may protect against becoming overweight or obese; however, the cross-sectional design of the study does not allow conclusions about the causality of the association.

Consumption of whole-grain cereals during weight loss: effects on dietary quality, dietary fiber, magnesium, vitamin B-6, and obesity
Melanson KJ, Angelopoulos TJ, Nguyen VT, Martini M, Zukley L, Lowndes J, Dube TJ, Fiutem JJ, Yount BW, Rippe JM. J Am Diet Assoc. 2006 Sep;106(9):1380-8; quiz 1389-90.

OBJECTIVE: While various weight-management approaches produce weight loss, they may differ in dietary quality. We monitored changes in nutrient intakes in overweight and obese subjects on three different weight-management programs.

DESIGN: Randomized clinical trial (pilot study) with two 12-week phases: phase 1, weekly counseling; phase 2, monitoring only.

SUBJECTS/SETTING: One hundred eighty nonsmoking, sedentary overweight and obese adults began this outpatient study; 134 (body mass index [calculated as kg/m(2)]=30.9+/-2.4; age=42.3+/-1.2 years) were used in analyses.

INTERVENTION: Twenty-four weeks of exercise only (control group), hypocaloric diet plus exercise, or hypocaloric diet with fiber-rich whole-grain cereals plus exercise.

MAIN OUTCOME MEASURES: At weeks 0, 12, and 24, diet quality was assessed by 3-day food records and body weight was measured.

STATISTICAL ANALYSES PERFORMED: Three-way analysis of variance with repeated measures.

RESULTS: The hypocaloric diet with fiber-rich whole-grain cereals plus exercise decreased energy intake more than exercise only (P=0.032). By week 12, the hypocaloric diet with fiber-rich whole-grain cereals plus exercise and the hypocaloric diet plus exercise decreased total fat more than exercise only, which was sustained in the hypocaloric diet with fiber-rich whole-grain cereals plus exercise at 24 weeks (P<0.001). At weeks 12 and 24, the hypocaloric diet with fiber-rich whole-grain cereals plus exercise reduced saturated fat intake more than exercise only. The hypocaloric diet with fiber-rich whole-grain cereals plus exercise increased total fiber, insoluble fiber (both P<0.001), magnesium (P=0.004), and vitamin B-6 (P=0.002) intakes more than the hypocaloric diet plus exercise and exercise only. Calcium and vitamin E intakes were inadequate in all groups. Weight loss was similar in the hypocaloric diet with fiber-rich whole-grain cereals plus exercise and the hypocaloric diet plus exercise.

CONCLUSIONS: Weight-reduction strategies may be associated with reduced intake of micronutrients, such as calcium and vitamin E. However, a hypocaloric diet with fiber-rich whole-grain cereal is effective for improving or maintaining other aspects of dietary quality during weight loss.

+Glucose Tolerance, Insulin Response, Syndrome X and Diabetes

Dietary Fiber and Type 2 Diabetes

Type 2 diabetes is the most common form of diabetes. It is characterized by sustained high blood sugar levels. It tends to develop when the body can no longer produce enough of the hormone insulin to lower blood sugar to normal levels or cannot properly use the insulin that it does produce. There are several important factors that may help lower your risk for type 2 diabetes, such as maintaining a healthy weight, being physically active, and not smoking. Researchers are also trying to pinpoint any relevant dietary factors, one of which seems to be a high-fiber diet. The studies of male health professionals and female nurses both found that a diet high in cereal fiber was linked to a lower risk of type 2 diabetes.

When it comes to factors that increase the risk of developing diabetes, a diet low in cereal fiber and rich in high glycemic index foods (which cause big spikes in blood sugar) seems particularly bad. Both Harvard studies - of nurses and of male health professionals - found that this sort of diet more than doubled the risk of type 2 diabetes when compared to a diet high in cereal fiber and low in high glycemic index foods.

Foods that have a high glycemic index include potatoes, refined foods such as white bread, white rice, refined cereals (corn flakes, Cheerios), white spaghetti, and sugar. Foods with a low glycemic index do not raise blood sugar levels as quickly and, therefore, are associated with a lower risk of type 2 diabetes. Low glycemic index foods include legumes, whole fruits, oats, bran, and whole-grain cereals. For more information, visit the glycemic index page.

References

· Fung TT, Hu FB, Pereira MA, et al. Whole-grain intake and the risk of type 2 diabetes: a prospective study in men. Am J Clin Nutr 2002; 76:535-40.
· Liu S, Willett WC, Stampfer MJ, et al. A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. Am J Clin Nutr 2000; 71:1455-61.
· Schulze MB, Liu S, Rimm EB, Manson JE, Willett WC, Hu FB. Glycemic index, glycemic load, and dietary fiber intake and incidence of type 2 diabetes in younger and middle-aged women. Am J Clin Nutr 2004; 80:348-56.

+High Blood Cholesterol and Heart Disease

The Effects of Dietary Fiber on High Cholesterol and Heart Disease

In the United States, coronary heart disease is a leading cause of death for both men and women. This disease is characterized by a buildup of cholesterol-filled plaque in the coronary arteries — the arteries that feed the heart. This causes them to become hard and narrow, a process referred to as atherosclerosis. Total blockage of a coronary artery produces a heart attack.

High intake of dietary fiber has been linked to a lower risk of heart disease in a number of large studies that followed people for many years. In a Harvard study of over 40,000 male health professionals, researchers found that a high total dietary fiber intake was linked to a 40 percent lower risk of coronary heart disease, compared to a low fiber intake. Cereal fiber, the fiber found in grains, seemed particularly beneficial. A related Harvard study of female nurses produced quite similar findings.

Fiber intake has also been linked with the metabolic syndrome, a constellation of factors that increases the chances of developing heart disease and diabetes. These factors include high blood pressure, high insulin levels, excess weight (especially around the abdomen), high levels of triglycerides, the body's main fat-carrying particle, and low levels of HDL (good) cholesterol. Several studies suggest that higher intake of fiber may somehow ward off this increasingly common syndrome.

+Breast Cancer

Dietary fibre and risk of breast cancer in the UK Women’s Cohort Study
Janet Elizabeth Cade, Victoria Jane Burley, Darren Charles Greenwood and the UK Women’s Cohort Study Steering Group

Background: Reports of relationships between dietary fibre intake and breast cancer have been inconsistent. Previous cohort studies have been limited by a narrow range of intakes.

Methods: Women who developed invasive breast cancer, 350 post-menopausally and 257 pre-menopausally, during 240 959 person-years of follow-up in the UK Women’s Cohort Study (UKWCS) were studied. This cohort has 35 792 subjects with a wide range of exposure to dietary fibre with intakes of total fibre in the lowest quintile of <20 g/day up to >30 g/day in the top quintile. Fibre and breast cancer relationships were explored using Cox regression modeling adjusted for measurement error. Effects of fibre, adjusting for confounders were examined for pre- and post-menopausal women separately.

Results: In pre-menopausal, but not post-menopausal women a statistically significant inverse relationship was found between total fibre intake and risk of breast cancer (P for trend=0.01). The top quintile of fibre intake was associated with a hazard ratio of 0.48 [95% confidence interval (CI) 0.24–0.96] compared with the lowest quintile. Pre-menopausally, fibre from cereals was inversely associated with risk of breast cancer (P for trend=0.05) and fibre from fruit had a borderline inverse relationship (P for trend=0.09). A further model including dietary folate strengthened the significance of the inverse relationship between total fibre and pre-menopausal breast cancer.

Conclusions: These findings suggest that in pre-menopausal women, total fibre is protective against breast cancer; in particular, fibre from cereals and possibly fruit.

Read Full Article of Dietary fibre and risk of breast cancer in the UK Women’s Cohort Study

Fiber, Estrogen and Breast Cancer in Mexican American Women
University of Southern California, Investigator(s): Malcolm Pike, Ph.D.

Research Priorities: Prevention and Risk Reduction, Explaining nutritional pathways for prevention of breast cancer

Initial Abstract (2002)

There is a large and compelling body of evidence (both epidemiological and experimental) implicating estrogen in the cause of human breast cancer. The role of diet in breast cancer risk is less clear. However, there is evidence to suggest that dietary fiber may play an important role in estrogen metabolism and may therefore be an important determinant of circulating estrogen levels in the body. Thus, understanding the biological relationship between dietary fiber intake and estrogen metabolism may provide some insight in how diet may alter a woman's risk of breast cancer.

We propose to investigate the hypothesis that high intake of dietary fiber, either total or a specific fraction (e.g., soluble fiber from legumes or insoluble fiber from grain), lowers estrogen levels in the body and thus lowers a woman's risk of breast cancer. We will be examining this hypothesis among a group of Mexican American Latinas currently enrolled in an ongoing research study. These women are a scientifically important group to study, because they have the lowest breast cancer rates of any major racial/ethnic group in the US, and their dietary fiber intake is higher than what is reported by other racial/ethnic groups.

Two generations of Mexican-origin postmenopausal women numbering nearly 7,000 are currently enrolled in an ongoing cohort study. Baseline data on dietary fiber have been collected and blood and urine specimens are currently being collected as part of an NIH funded grant. No additional subject recruitment will be required for this proposed study. We will compare dietary fiber intake, quantified from both a food frequency questionnaire and from a biochemical marker of intake, with blood hormone levels. An updated food frequency questionnaire will be administered at the time of blood draw to obtain current dietary information.

Epidemiology studies examining dietary fiber and breast cancer risk are equivocal. Investigators have proposed that the reason may be due to the heterogeneous nature of dietary fiber, differences in ways fiber is measured and quantified, or the magnitude of fiber intake in the populations studied. This study is innovative in that it (1) utilizes an ideal population where the traditional diet is rich in dietary fiber; (2) comprises two generations of Mexican origin women where differences in breast cancer rates provide powerful evidence on the extent to which the causes are due to changes in environmental factors; and (3) utilizes two methods of quantifying fiber intake - that of a food frequency questionnaire as well as a biochemical marker.

Final Report (2004)

There is a large and compelling body of evidence implicating estrogen in the cause of human breast cancer. The role of diet in breast cancer risk is less clear. There is evidence to suggest that dietary fiber may play an important role in estrogen metabolism and may be an important determinant of circulating estrogen levels in the body. Understanding the biological relationship between dietary fiber intake and estrogen metabolism may provide some insight in how diet may alter a woman's risk of breast cancer.

This study investigated the hypothesis that high dietary fiber intake, either total or a specific fraction (e.g., soluble or insoluble non-starch polysaccharides (NSP) or total lignan), lowers circulating estrogen levels. We investigated this hypothesis among Latinas of Mexican origin enrolled in "The Multiethnic/Minority Cohort Study of Diet and Cancer." Women, who were aged 45-64 at cohort entry, reported never having used menopausal hormone therapy (HT) and reported being postmenopausal on the baseline questionnaire, were eligible for selection. The dietary fiber value from the baseline food frequency questionnaire (FFQ) was used to further define subjects for inclusion to ensure a sufficient number of subjects in both the high and low comparison groups. Subjects agreeing to participate in this sub-study were asked to provide a blood specimen as well as fill out a second complete FFQ in order to provide current dietary information concurrent with blood collection. Plasma levels of enterolactone and genistein were measured in the Folkhalsan Research Center laboratory at the University of Helsinki, Finland and serum hormone assays were conducted in the Reproductive Endocrine Research Laboratory at USC.

Blood specimens from 353 Latina women who met the inclusion criteria for the study were included in laboratory assays. The first aim of this study was to determine the effect of dietary fiber intake on blood concentration levels of estrone (E1), estradiol (E2), and sex-hormone-binding globulin (SHBG). Dietary fiber intake was quantified in two ways: (1) from the FFQ administered at time of blood draw; and (2) from biomarkers of dietary fiber intake, i.e., the lignan enterolactone (Enl) and the isoflavone genistein. We found that measures of dietary fiber intake, quantified from the FFQ administered at time of blood draw, as well as the biomarkers Enl and genistein were significantly associated with serum hormone levels. As predicted, serum E1 and E2 levels decreased, as did bioavailable E2, as dietary fiber intake increased. These associations remained after adjusting for weight, even though weight strongly influenced the blood levels of E1, E2, bioavailable E2, SHBG, and fiber in opposite directions. This provides strong evidence of an association between dietary fiber intake and circulating hormone levels in postmenopausal women. We are continuing to investigate these associations to learn which component of dietary fiber, e.g., insoluble fiber from grain or soluble fiber from legumes, has the strongest influence.

A secondary aim of this study was to investigate the correlations between plasma Enl and genistein with various measures of dietary fiber intake measured by the FFQ. We found a statistically significant positive correlation (0.14) between plasma Enl and the lignan secoisolariciresinol quantified from the FFQ. Plasma genistein was significantly correlated with dietary fiber (0.18), soluble NSP (0.16), insoluble NSP (0.18), and the lignan secoisolariciresinol (0.14).

This study provides an exceptional opportunity to understand the biological relationship between dietary fiber and estrogen metabolism and potentially provides a dietary mechanism for lowering a woman's risk of breast cancer.

+Coronary Heart Disease

Dietary Fiber and Coronary Heart Disease

References

· Pereira MA, O'Reilly E, Augustsson K, et al. Dietary fiber and risk of coronary heart disease: a pooled analysis of cohort studies. Arch Intern Med 2004; 164:370-6.
· Van Horn L. Fiber, lipids, and coronary heart disease. A statement for healthcare professionals from the Nutrition Committee, American Heart Association. Circulation 1997; 95:2701-4.<
· Rimm EB, Ascherio A, Giovannucci E, Spiegelman D, Stampfer MJ, Willett WC. Vegetable, fruit, and cereal fiber intake and risk of coronary heart disease among men. JAMA 1996; 275:447-51.
· Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr 1999; 69:30-42.
· McKeown NM, Meigs JB, Liu S, Saltzman E, Wilson PW, Jacques PF. Carbohydrate nutrition, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort. Diabetes Care 2004; 27:538-46.
· McKeown NM, Meigs JB, Liu S, Wilson PW, Jacques PF. Whole-grain intake is favorably associated with metabolic risk factors for type 2 diabetes and cardiovascular disease in the Framingham Offspring Study. Am J Clin Nutr 2002; 76:390-8.

+Gastrointestinal Disorders

+Constipation and Hemorrhoids

Dietary Fiber and Constipation

Constipation is the most common gastrointestinal complaint in the United States and is of particular concern to the elderly. The gastrointestinal tract is highly sensitive to dietary fiber, and consumption of fiber seems to relieve and prevent constipation. The fiber in wheat bran and oat bran seems to be more effective than similar amounts of fiber from fruits and vegetables. Experts recommend increasing fiber intake gradually rather than suddenly. The intake of beverages should also be increased, as fiber absorbs water.

Wondering how much water or other beverages you should drink a day? The Institute of Medicine gives the following general recommendations for water consumption: Women generally need to consume 91 ounces of water each day from beverages and foods, while men generally need to consume 125 ounces each day. People typically obtain about 80 percent of their water from beverages (including beverages that contain caffeine) and 20 percent of their water from foods. So for women, that translates into drinking 9 8-oz. glasses of water or other beverages each day and obtaining another 18 ounces of water from foods; for men, that translates into drinking roughly 12 8-oz. glasses of water or other beverages each day, and obtaining another 25 ounces of water from foods.

Reference

· Institute of Medicine. Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate. 2004. Washington, D.C.: The National Academies Press.

+Inflammatory Bowel Disease

Influence of dietary fiber on inflammatory bowel disease and colon cancer: importance of fermentation pattern. Rose DJ, DeMeo MT, Keshavarzian A, Hamaker BR. Nutr Rev. 2007 Feb;65(2):51-62.

The benefits of dietary fiber on inflammatory bowel disease may be related to the fermentative production of butyrate in the colon, which appears to decrease the inflammatory response. The benefits of dietary fiber against colon cancer may be related to both fermentative and non-fermentative processes, although poorly fermentable fibers appear more influential. Dietary fiber fermentation profiles are important in determining optimal fibers for colonic health, and may be a function of structure, processing conditions, and other food components. A greater understanding of the relationships between fermentation rate and dietary fiber structure would allow for development of dietary fibers for optimum colonic health.

Effects of dietary fiber on inflammatory bowel disease. Galvez J, Rodríguez-Cabezas ME, Zarzuelo A. Mol Nutr Food Res. 2005 Jun;49(6):601-8.

The chronic idiopathic inflammatory bowel diseases (IBDs), namely Crohn's disease and ulcerative colitis, appear to be derived from an inappropriate reaction towards a luminal agent, most probably driven by the intestinal microflora, which upregulates the synthesis and release of different pro-inflammatory mediators, thus contributing to tissue damage that characterizes these intestinal conditions. Several studies have reported that IBD is associated with impairment in short-chain fatty acid (SCFA) production, mainly acetate, propionate, and butyrate. They are produced in the large bowel by anaerobic bacterial fermentation of undigested dietary carbohydrates and fiber polysaccharides, with butyrate being considered as the major fuel source for colonocytes. These SCFAs have been proposed to play a key role in the maintenance of colonic homeostasis. Therefore, it is reasonable to consider therapeutic approaches that increase colonic SCFA production, as it can be achieved by administration of dietary fiber to IBD patients. Unfortunately, there is quite limited documentation of efficacy of dietary fiber in properly designed trials. This review discusses the rationale, available evidence for the use of dietary fiber and its mechanisms of action in the treatment and prevention of IBDs.

+Ulcerative Colitis

Randomized clinical trial of Plantago ovata seeds (dietary fiber) as compared with mesalamine in maintaining remission in ulcerative colitis.
Fernández-Bañares F, Hinojosa J, Sánchez-Lombraña JL, Navarro E, Martínez-Salmerón JF, García-Pugés A, González-Huix F, Riera J, González-Lara V, Domínguez-Abascal F, Giné JJ, Moles J, Gomollón F, Gassull MA. Spanish Group for the Study of Crohn's Disease and Ulcerative Colitis (GETECCU). Am J Gastroenterol. 1999 Feb;94(2):427-33.

OBJECTIVE: Butyrate enemas may be effective in the treatment of active distal ulcerative colitis. Because colonic fermentation of Plantago ovata seeds (dietary fiber) yields butyrate, the aim of this study was to assess the efficacy and safety of Plantago ovata seeds as compared with mesalamine in maintaining remission in ulcerative colitis.

METHODS: An open label, parallel-group, multicenter, randomized clinical trial was conducted. A total of 105 patients with ulcerative colitis who were in remission were randomized into groups to receive oral treatment with Plantago ovata seeds (10 g b.i.d.), mesalamine (500 mg t.i.d.), and Plantago ovata seeds plus mesalamine at the same doses. The primary efficacy outcome was maintenance of remission for 12 months.

RESULTS: Of the 105 patients, 102 were included in the final analysis. After 12 months, treatment failure rate was 40% (14 of 35 patients) in the Plantago ovata seed group, 35% (13 of 37) in the mesalamine group, and 30% (nine of 30) in the Plantago ovata plus mesalamine group. Probability of continued remission was similar (Mantel-Cox test, p = 0.67; intent-to-treat analysis). Therapy effects remained unchanged after adjusting for potential confounding variables with a Cox's proportional hazards survival analysis. Three patients were withdrawn because of the development of adverse events consisting of constipation and/or flatulence (Plantago ovata seed group = 1 and Plantago ovata seed plus mesalamine group = 2). A significant increase in fecal butyrate levels (p = 0.018) was observed after Plantago ovata seed administration.

CONCLUSIONS: Plantago ovata seeds (dietary fiber) might be as effective as mesalamine to maintain remission in ulcerative colitis.

+Gallstones

The Effect of Dietary Fiber on Gallstones

What are gallstones?

Gallstones are small, pebble-like substances that develop in the gallbladder. The gallbladder is a small, pear-shaped sac located below your liver in the right upper abdomen. Gallstones form when liquid stored in the gallbladder hardens into pieces of stone-like material. The liquid—called bile—helps the body digest fats. Bile is made in the liver, then stored in the gallbladder until the body needs it. The gallbladder contracts and pushes the bile into a tube—called the common bile duct—that carries it to the small intestine, where it helps with digestion.

Bile contains water, cholesterol, fats, bile salts, proteins, and bilirubin—a waste product. Bile salts break up fat, and bilirubin gives bile and stool a yellowish-brown color. If the liquid bile contains too much cholesterol, bile salts, or bilirubin, it can harden into gallstones.

The two types of gallstones are cholesterol stones and pigment stones. Cholesterol stones are usually yellow-green and are made primarily of hardened cholesterol. They account for about 80 percent of gallstones. Pigment stones are small, dark stones made of bilirubin. Gallstones can be as small as a grain of sand or as large as a golf ball. The gallbladder can develop just one large stone, hundreds of tiny stones, or a combination of the two.

The gallbladder and the ducts that carry bile and other digestive enzymes from the liver, gallbladder, and pancreas to the small intestine are called the biliary system.

Gallstones can block the normal flow of bile if they move from the gallbladder and lodge in any of the ducts that carry bile from the liver to the small intestine. The ducts include the

· hepatic ducts, which carry bile out of the liver
· cystic duct, which takes bile to and from the gallbladder
· common bile duct, which takes bile from the cystic and hepatic ducts to the small intestine

Bile trapped in these ducts can cause inflammation in the gallbladder, the ducts, or in rare cases, the liver. Other ducts open into the common bile duct, including the pancreatic duct, which carries digestive enzymes out of the pancreas. Sometimes gallstones passing through the common bile duct provoke inflammation in the pancreas—called gallstone pancreatitis—an extremely painful and potentially dangerous condition.

If any of the bile ducts remain blocked for a significant period of time, severe damage or infection can occur in the gallbladder, liver, or pancreas. Left untreated, the condition can be fatal. Warning signs of a serious problem are fever, jaundice, and persistent pain.

What causes gallstones?

Scientists believe cholesterol stones form when bile contains too much cholesterol, too much bilirubin, or not enough bile salts, or when the gallbladder does not empty completely or often enough. The reason these imbalances occur is not known.

The cause of pigment stones is not fully understood. The stones tend to develop in people who have liver cirrhosis, biliary tract infections, or hereditary blood disorders—such as sickle cell anemia—in which the liver makes too much bilirubin.

The mere presence of gallstones may cause more gallstones to develop. Other factors that contribute to the formation of gallstones, particularly cholesterol stones, include

· Sex. Women are twice as likely as men to develop gallstones. Excess estrogen from pregnancy, hormone replacement therapy, and birth control pills appears to increase cholesterol levels in bile and decrease gallbladder movement, which can lead to gallstones.
· Family history. Gallstones often run in families, pointing to a possible genetic link.
· Weight. A large clinical study showed that being even moderately overweight increases the risk for developing gallstones. The most likely reason is that the amount of bile salts in bile is reduced, resulting in more cholesterol. Increased cholesterol reduces gallbladder emptying. Obesity is a major risk factor for gallstones, especially in women.
· Diet. Diets high in fat and cholesterol and low in fiber increase the risk of gallstones due to increased cholesterol in the bile and reduced gallbladder emptying.
· Rapid weight loss. As the body metabolizes fat during prolonged fasting and rapid weight loss—such as “crash diets”—the liver secretes extra cholesterol into bile, which can cause gallstones. In addition, the gallbladder does not empty properly.
· Age. People older than age 60 are more likely to develop gallstones than younger people. As people age, the body tends to secrete more cholesterol into bile.
· Ethnicity. American Indians have a genetic predisposition to secrete high levels of cholesterol in bile. In fact, they have the highest rate of gallstones in the United States. The majority of American Indian men have gallstones by age 60. Among the Pima Indians of Arizona, 70 percent of women have gallstones by age 30. Mexican American men and women of all ages also have high rates of gallstones.
· Cholesterol-lowering drugs. Drugs that lower cholesterol levels in the blood actually increase the amount of cholesterol secreted into bile. In turn, the risk of gallstones increases.
· Diabetes. People with diabetes generally have high levels of fatty acids called triglycerides. These fatty acids may increase the risk of gallstones.

Courtesy of National Digestive Diseases Information Clearinghouse

The Effect of Dietary Fiber on Gallstones
From the Handbook of Dietary Fiber, by Sungsoo Cho, Mark L. Dreher, 2001

Epidemiological evidence shows an inverse relationship between dietary fiber level and incidence of gallstones (Pilch, 1987). The incidence of gallstones is markedly higher in urban, Westernized societies than in primitive, rural societies where diets contain a higher proportion of fiber (Heaton and Pomare, 1974). Vegetarians have been found to exhibit a lower incidence of gallstones (Niar and Mayberry, 1994). A possible mechanism by which fiber inhibits the formation of gallstones is that fiber-depleted foods encourage overnutrition and hyperinsulimia, i.e., that fiber-depleted sugar evokes a greater insulin response.

Although some clinical studies have not found a preventive effect of dietary fiber on gallstone disease (Diehl et al., 1989), several studies have confirmed the role of fiber in preventing gallstone disease (Zhang et al., 1992). Studies have sown that humans with gallstones or highly lithogenic bile tend to improve when fed wheat bran, while normal persons are not affected (Hayes et al., 1992). Animal studies have also demonstrated a role of insoluble and soluble fibers in protecting against gallstone formation.

After reviewing the scientific evidence concerning the effect of dietary fiber on gallstone formation, Heaton and Pomare (1974) concluded that a low intake of wheat bran or similar cereal fiber is likely to promote gallstones. Published studies show that increased intake of wheat bran reduces the percentage of deoxycholic acid content and cholesterol content in bile acids. Deoxycholic acid has been shown to be a risk factor for bile supersaturated with cholesterol and hence for gallstones. LSRO and the NRC concluded similarly that supplemental wheat bran can lower both the cholesterol saturation index and the deoxycholic acid content of bile. LSRO concluded, however that the influence of dietary fiber on gallstone formation is still unresolved.

Metabolic Effects of Dietary Fiber
David Kritchevsky, PhD at the Symposium on Clinical Nutrition

Gallstones can be induced in hamsters by feeding a diet containing 74 percent glucose, 20 percent casein, salt mix, vitamin mix and choline chloride. The diet need not contain either fat or cholesterol. Replacement of the glucose with rice starch reduces gallstone formation almost to zero. Bergman and van der Linden fed this type of diet to hamsters and augmented it with 5 percent pectin, lignin or psyllium colloid. None of the hamsters fed lignin or psyllium were found to have gallstones, 29 percent of those fed pectin had gallstones, whereas 58 percent of the controls had gallstones. Gallstones formed in mice fed a lithogenic diet were dissolved when the mice were returned to laboratory ration. Rabbits fed a semipurified diet containing 30 percent casein and 15 percent beef tallow exhibited gallstones (3/5) but when 5 percent pectin was added to the diet no gallstones were observed. It has been suggested that a diminished bile acid pool plays a role in cholelithiasis in man.

Nigerians ingesting a high fiber diet have increased bile acid pool size and increased bile acid synthesis rates compared with populations eating a "Western" diet. Pomare, Heaton and associates showed that when patients with gallstones were fed wheat bran (an average of 57 grams per day) their chenodeoxycholic acid pool increased significantly, the deoxycholic acid pool fell and the cholesterol saturation of their bile diminished.

The mechanism of action of fiber in affecting cholelithiasis is unknown, but it may be related to the increases in bile acid pool size that have been observed in rats6' and monkeys.

Spontaneous gallstone formation in deer mice: Interaction of cholesterol, bile acids, and dietary fiber
GINNETT Dorothy A., THEIS Jerold H., KANEKO J. Jerry, Journal of wildlife diseases (J. wildl. dis.) ISSN 0090-3558, 2003, vol. 39, no.1, pp. 105-113

Abstract A study of the physiologic and ecologic factors involved in a spontaneous seasonal gallstone cycle of deer mice (Peromyscus maniculatus gambelii) was conducted at the Tulelake National Wildlife Refuge (California, USA) from March 1991 to June 1992. The specific hypothesis examined was whether or not seasonal increases in dietary fiber intake provides the necessary conditions for a solubility defect, or supersaturation mechanism, resulting in precipitation of cholesterol gallstones.

Results indicated that in addition to the seasonal gallstone prevalence cycle, these deer mice exhibit significant seasonal cycling in serum cholesterol, serum bile acids, fecal bile acids, and diet composition. These physiologic and dietary cycles were phase-advanced 3 mo over the gallstone prevalence cycle, indicating an approximate 3 mo time period for gallstone formation under field conditions.

Further, seasonal dietary fiber (plant material and seeds) was positively correlated with both serum cholesterol and the fecal bile acids. This suggests that in wild deer mice, variations in dietary fiber may significantly affect the resorption of bile acids. thereby providing a potential physiologic and nutritional mechanism for spontaneous cholesterol gallstone formation.

+Diverticulitis

Dietary Fiber and Diverticular Disease

Diverticulitis, an inflammation of the intestine that in Western society is one of the most common age-related disorders of the colon. In North America, this painful disease is estimated to occur in one-third of all those over age 45 and in two-thirds of those over age 85.

High fiber intakes are associated with decreased risk of diverticulosis, a relatively common condition that is characterized by the formation of small pouches (diverticula) in the colon. Although most people with diverticulosis experience no symptoms, about 15-20% may develop pain or inflammation, known as diverticulitis. In a large prospective cohort study, men with the highest dietary fiber intakes had a risk of developing symptomatic diverticular disease that was 42% lower than men with the lowest dietary fiber intakes. The protective effect of dietary fiber against diverticular disease was strongest for nonviscous dietary fiber, particularly cellulose.

Courtesy of the Linus Pauling Institute, Oregon State University

Preventing diverticular disease. Review of recent evidence on high-fibre diets. Aldoori W, Ryan-Harshman M. Can Fam Physician, 2002 Oct;48:1632-7.

OBJECTIVE: To review recent evidence on dietary factors associated with diverticular disease (DD) with special emphasis on dietary fibre.

QUALITY OF EVIDENCE: MEDLINE was searched from January 1966 to December 2001 for articles on the relationship between dietary and other lifestyle factors and DD. Most articles either focused on dietary intervention in treating symptomatic DD or were case-control studies with inherent limitations for studying diet-disease associations. Only one large prospective study of male health professionals in the United States assessed diet at baseline and before initial diagnosis of DD.

MAIN MESSAGE: A diet high in fibre mainly from fruits and vegetables and low in total fat and red meat decreases risk of DD. Evidence indicates that the insoluble component of fibre is strongly associated with lower risk of DD; this association was particularly strong for cellulose. Caffeine and alcohol do not substantially increase risk of DD, nor does obesity, but higher levels of physical activity seem to reduce risk of DD.

CONCLUSION: A diet high in fibre and low in total fat and red meat and a lifestyle with more physical activity might help prevent DD.

+Colon Cancer

The Effect of Dietary Fiber on Colon Cancer

Dietary fiber and whole-grain consumption in relation to colorectal cancer in the NIH-AARP Diet and Health Study.
Schatzkin A, Mouw T, Park Y, Subar AF, Kipnis V, Hollenbeck A, Leitzmann MF, Thompson FE. Am J Clin Nutr. 2007 May;85(5):1353-60.

BACKGROUND: Whether the intake of dietary fiber can protect against colorectal cancer is a long-standing question of considerable public health import, but the epidemiologic evidence has been inconsistent.

OBJECTIVE: The objective was to investigate the relation between dietary fiber and whole-grain food intakes and invasive colorectal cancer in the prospective National Institutes of Health-AARP Diet and Health Study.

DESIGN: The analytic cohort consisted of 291,988 men and 197,623 women aged 50-71 y. Diet was assessed with a self-administered food-frequency questionnaire at baseline in 1995-1996; 2974 incident colorectal cancer cases were identified during 5 y of follow-up. The Cox proportional hazards model was used to estimate the relative risks (RRs) and 95% CIs.

RESULTS: Total dietary fiber intake was not associated with colorectal cancer. The multivariate RR for the highest compared with the lowest intake quintile (RR(Q5-Q1)) was 0.99 (95% CI: 0.85, 1.15; P for trend = 0.96). In analyses of fiber from different food sources, only fiber from grains was associated with a lower risk of colorectal cancer (multivariate RR(Q5-Q1): 0.86; 95% CI: 0.76, 0.98; P for trend = 0.01). Whole-grain intake was inversely associated with colorectal cancer risk: the multivariate RR(Q5-Q1) was 0.79 (95% CI: 0.70, 0.89) for the whole cohort (P for trend < 0.001). The association with whole grain was stronger for rectal than for colon cancer.

CONCLUSIONS: In this large prospective cohort study, total dietary fiber intake was not associated with colorectal cancer risk, whereas whole-grain consumption was associated with a modest reduced risk.

+Additional Resources

+Article: Fiber and your Child

Fiber and your Child
Courtesy of KidsHealth.org

Few children - even the most nutrition conscious - would say they crave a good fiber-rich meal. Although the thought of fiber might elicit gags and groans in kids of all ages, a plethora of appetizing foods are actually good sources of fiber - from many fruits to whole-grain cereals. And your child is probably eating them without even knowing it.

Not just for the senior-citizen crowd, foods that are good sources of fiber are beneficial because they're filling and, therefore, discourage overeating - even though fiber itself adds no calories. Plus, when combined with drinking adequate fluids, eating high-fiber fare helps move food through the digestive system and protect against gut cancers and constipation. It may also lower LDL cholesterol ("bad" cholesterol) as well as help prevent diabetes and heart disease.

Figuring Out Fiber

Listed on food labels under total carbohydrates, dietary fiber is found in plant foods like fruits, vegetables, and grains. Some of the best sources are:

· whole-grain breads and cereals (which have more fiber than white bread and white rice)
· apples
· oranges
· bananas
· berries
· prunes
· pears
· green peas
· legumes (split peas, soy, lentils, etc.)
· artichokes
· almonds

A high-fiber food has 5 grams or more of fiber per serving and a good source of fiber is one that provides 2.5 to 4.9 grams per serving. Here's how some fiber-friendly foods stack up:

· 1/2 cup (118 milliliters) of cooked navy beans (9.5 grams of fiber)
· 1/2 cup (118 milliliters) of cooked lima beans (6.6 grams)
· 1 medium baked sweet potato with peel (4.8 grams)
· 1 whole-wheat English muffin (4.4 grams)
· 1/2 cup (118 milliliters) of cooked green peas (4.4 grams)
· 1 medium raw pear with skin (4 grams)
· 1/2 cup (118 milliliters) of raw raspberries (4 grams)
· 1 medium baked potato with skin (3.8 grams)
· 1/4 cup (59 milliliters) of oat bran cereal (3.6 grams)
· 1 ounce (28 grams) of almonds (3.3 grams)
· 1 medium raw apple with skin (3.3 grams)
· 1/2 cup (118 milliliters) of raisins (3 grams)
· 1/4 cup (59 milliliters) of baked beans (3 grams)
· 1 medium orange (3 grams)
· 1 medium banana (3 grams)
· 1/2 cup (118 milliliters) canned sauerkraut (3 grams)

A simple way to determine how many grams of fiber your child should be consuming each day is to add 5 to your child's age in years (i.e., a 5-year-old should get about 10 grams of fiber). After the age of 15, kids (and adults) need about 20 to 25 grams of fiber per day.

Making Fiber Part of Your Family's Diet

Although many kids often cringe at the mere mention of fiber, they're probably eating fiber every day without even realizing that it's so good for them. And there are plenty of creative, fun, and even tasty ways to incorporate - even sneak - these fiber-rich foods into your child's diet:

Breakfast

· Make oatmeal (a whole grain) part of your kids' morning meals.
· Opt for whole-wheat or other whole-grain cereals that list ingredients such as whole wheat or oats as one of the first few items on the ingredient list.
· Make pancakes with whole-grain (or buckwheat) pancake mix and top with apples, berries, or raisins.
· Serve bran or whole grain waffles topped with fruit.
· Offer whole-wheat bagels or English muffins, instead of white toast.
· Serve whole-grain cereals. Many popular cereals are made with whole grains, but try to choose ones that have less sugar than some of the excessively sweet whole-grain cereal offerings.
· Top fiber-rich cereal with apples, oranges, berries, or bananas. Add almonds to pack even more fiber punch.
· Mix your child's favorite cereal with a fiber-rich one or top it with a tablespoon of bran.

Lunch and Dinner

· Make sandwiches with whole-grain breads (rye, oat, or wheat), instead of white.
· Make a fiber-rich sandwich with whole-grain bread, peanut butter, and bananas.
· Serve whole-grain rolls with dinner, instead of white rolls.
· Use whole-grain spaghetti and other pastas, instead of white.
· Serve wild or brown rice with meals, instead of white rice. Add beans (kidney, black, navy, and pinto) to rice dishes for even more fiber.
· Spice up salads with berries and almonds, chickpeas, cooked artichokes, and beans (kidney, black, navy, or pinto).
· Use whole-grain (corn or whole wheat) soft-taco shells or tortillas to make burritos or wraps. Fill them with eggs and cheese for breakfast; turkey, cheese, lettuce, tomato, and light dressing for lunch; and beans, salsa, taco sauce, and cheese for dinner.
· Add lentils or whole-grain barley to your child's favorite soups.
· Create mini-pizzas by topping whole-wheat English muffins or bagels with pizza sauce, low-fat cheese, mushrooms, and chunks of grilled chicken.
· Add bran to meatloaf or burgers. (The trick is not to add too much bran, or the food will taste like sawdust and your family might catch on!)
· Serve sweet potatoes, with the skins, as tasty side dishes. Regular baked potatoes, with the skins, are good sources of fiber, too.
· Top low-fat hot dogs or veggie dogs with sauerkraut and serve them on whole-wheat hot dog buns.
· Include fresh fruit as part of your child's packed school lunch. Pears, apples, bananas, oranges, and berries are all high in fiber.

Snacks and Treats

· Bake cookies or muffins using whole-wheat flour, instead of regular. Or use some whole-wheat and some regular flour, so that the texture of your baked treats won't be drastically different from what your child is used to. Add raisins, berries, bananas, or chopped or pureed apples to the mix for even more fiber.
· Add bran to baking items such as cookies and muffins.
· Top whole-wheat crackers with peanut butter or low-fat cheese.
· Offer popcorn - a whole-grain food - as a mid-day treat or while your child watches TV or movies. Aim for popcorn without lots of added fat or sugar. (However, only give popcorn to kids over 4 years old because the popular snack can be a choking hazard.)
· Top ice cream, frozen yogurt, or regular yogurt with whole-grain cereal, berries, or almonds for some added nutrition and crunch.
· Serve apples topped with peanut butter.
· Make fruit salad with pears, apples, bananas, oranges, and berries. Top with almonds for added crunch. Serve as a side dish with meals or alone as a snack.
· Make low-fat breads, muffins, or cookies with canned pumpkin.
· Leave the skins on when giving your child fruits and veggies as snacks or as part of a meal.

However you choose to incorporate fiber into your child's regular diet, don't push fiber on your family. Instead of introducing high-fiber foods and ingredients into your child's meals and snacks immediately, make gradual changes that will add up to a diet that's higher in fiber over time.

And it's not all about making your child try to like foods - from prunes to bran, from split peas to lima beans - that many kids often find unappealing. Just offer your family plenty of things they likely never imagined are good sources of fiber - fruits like pears and berries, vegetables like beans and peas, and whole-grain breakfast cereals that they're probably already getting as their regular diet. Not only will your child be getting the fiber he or she needs, you'll be setting the tone for a lifetime of healthy eating.

+Article: Diverticulosis, an Ill of the Affluent Life

Personal Health: Diverticulosis, an Ill of the Affluent Life
By Jane E. Brody, NY Times, 2002

Let me start with some good news for the many millions of people who have been told that they have diverticulosis and should avoid eating foods containing small seeds and that they should never eat nuts. It turns out that this longstanding bit of medical wisdom was based on virtually no scientific evidence, just guesswork, and unless you have already developed inflamed or infected diverticula, your diet need not be so restricted, most experts say.

You no longer have to seed tomatoes, you can enjoy strawberries, raspberries and blueberries, and you can even eat nuts as long as you chew them thoroughly.

Now, just what is this condition and what should be done to prevent it and its complications?

People living in industrialized countries have paid some hefty health-related prices for their relatively affluent lives, like high rates of heart disease, cancer, obesity, diabetes and osteoporosis. But there is one extremely common health problem linked to affluence that few are aware of, unless they suddenly become seriously ill. That problem is diverticulosis, outpouchings in the large intestine resembling weakened areas in tire tubes.

The Vegetable-Rich Diet

Though common in well-developed countries, diverticular disease is virtually unknown in the poorer countries of Asia and Africa, where people subsist mainly on high-fiber vegetable-rich diets. Diverticulosis was unknown in this country too until the early 1900's, when Americans began moving away from fresh-from-the-earth high-fiber foods and instead adopted diets replete with processed foods made from refined flour lacking the fibrous bran in whole grains.

As American diets became richer in meats, fat, sugar and highly refined processed foods, the plates had less and less room for fruits, vegetables and whole grains. And despite years of efforts to get people to eat at least five servings a day of fruits and vegetables for their overall health, only about a third of Americans have taken the advice.

Dietary fiber -- both the soluble fibers found in foods like oats and many fruits and the insoluble ones in whole wheat, corn and virtually all plant foods -- helps to keep the stool soft and easy to eliminate. Diets lacking in adequate fiber often result in hard stools and constipation, prompting those afflicted to exert excess pressure on the colon when attempting a bowel movement. It is this pressure, repeated over and over through the years, that is believed to be the cause of diverticular pouches.

A third of Americans over 45, half of those 60 to 80 and virtually everyone over 90 has diverticular pouches. Many people with these pouches are unaware of their presence unless told about them by a doctor who has performed a colonoscopy, sigmoidoscopy or barium enema examination, usually for some other reason. But for 10 percent to 25 percent of the people with diverticulosis, inflammation or infection can suddenly strike one or more of the pouches, causing intense pain and sometimes potentially fatal complications.

Prevention and Treatment

Of course, the best way to deal with diverticular disease is to avoid getting it in the first place, mainly by avoiding constipation and hard-to-move stools. The secret here is no secret -- eat more fiber (and drink more water to aid its passage through the digestive tract).

All the major organizations offering dietary advice suggest eating at least 25 grams of fiber a day, but few Americans now come anywhere near that amount. In addition to all fruits and vegetables, foods made from whole grains -- like whole wheat bread, brown rice and oats -- and all the dried peas and beans (cooked, of course) are excellent sources of dietary fiber.

Increasing dietary fiber is especially important for people who must take medication, like narcotic painkillers, or supplements, like calcium and iron, that tend to cause constipation.

The potential benefits of a high-fiber diet accrue not just to one's digestion. Dietary fiber also helps to prevent heart disease and stroke by lowering blood levels of cholesterol, it helps to maintain a stable blood sugar level and thus prevent adult-onset diabetes, and it helps a person achieve and maintain a normal body weight.

Dietary fiber gives people something for nothing. Since it passes through the digestive tract undigested, it enhances feelings of satiety without adding calories to a person's diet. In other words, fiber fills you up before it fills you out.

Among fiber-rich foods, the National Institutes of Health lists apples and pears (4 grams in a medium-size fruit), acorn squash (7 grams per 3/4 cup of cooked squash), kidney beans (6 grams in 1/2 cup) and bran flakes (5 grams per 3/4 cup). Other good sources of fiber include cabbage, spinach, broccoli, carrots, lima beans and soy foods.

Clearly, improving the plant food content of the diet is the most desirable approach. But for those who cannot eat enough high-fiber foods or for whom fiber-rich foods alone do not produce the desired outcome, there are now a number of over-the-counter fiber supplements available that can help. These products, mixed with liquid, supply 2 to 3 1/2 grams of fiber per tablespoon.

Take care, though, in adding fiber to your diet. Do it gradually to reduce the risk of developing painful intestinal gas. Give your gut a chance to get used to the new menu gradually.

Complications

Most people are never troubled by their diverticular pouches. But should a pouch become inflamed or infected -- a condition called diverticulitis, antibiotics are prescribed. Bed rest and a liquid fiber-free diet, plus pain medication, are commonly prescribed to give the bowel a chance to heal.

Once the problem abates, a gradual return to a high-fiber diet is recommended. But for patients who have had repeated attacks of diverticulitis after consuming foods containing seeds or nuts, the doctor is likely to suggest avoiding them.

Severe or frequent attacks of diverticulitis may be best treated surgically to remove the damaged part of the bowel. If neglected, an infected diverticula can cause complications, including abscesses, fistulas, peritonitis, intestinal obstruction, serious bleeding and perforations that allow toxic substances to seep into the abdomen.

These complications can become life-threatening and nearly always require emergency surgery. The surgeon may have to create a temporary colostomy -- a hole in the abdomen through which the bowel can empty -- until the infection or obstruction clears. Afterward, a second operation is done to reattach the ends of the colon and close the abdominal hole.

+Research Abstract: Effect of a high-fiber vs a fiber-supplemented diet on C-reactive protein level

Effect of a high-fiber diet vs a fiber-supplemented diet on C-reactive protein* level
King DE, Egan BM, Woolson RF, Mainous AG 3rd, Al-Solaiman Y, Jesri A. Arch Intern Med. 2007 Mar 12;167(5):502-6.

BACKGROUND: Diets high in fiber are associated with lower levels of inflammatory markers. This study examined the reduction in inflammation from a diet supplemented with fiber compared with a diet naturally high in fiber.

METHODS: Randomized crossover intervention trial of 2 diets, a high-fiber (30-g/d) Dietary Approaches to Stop Hypertension (DASH) diet or fiber-supplemented diet (30 g/d), after a baseline (regular) diet period of 3 weeks. There were 35 participants (18 lean normotensive and 17 obese hypertensive individuals) aged 18 to 49 years.

RESULTS: The study included 28 women and 7 men; 16 (46%) were black, the remainder white. The mean (SD) fiber intake on baseline diets was 11.9 (0.3) g/d; on the high-fiber DASH diet, 27.7 (0.6) g/d; and on the supplemented diet, 26.3 (0.4) g/d. Overall, the mean C-reactive protein (CRP) level changed from 4.4 to 3.8 mg/L (-13.7%; P = .046) in the high-fiber DASH diet group and to 3.6 mg/L (-18.1%) in the fiber-supplemented diet group (P = .03). However, CRP levels decreased in the 18 lean normotensive participants in either intervention diet group (2.0 mg/L [baseline] vs 1.4 mg/L [high-fiber DASH] vs 1.2 mg/L [supplemented]); P<.05) but did not change significantly (7.1 mg/L [baseline] vs 6.2 mg/L [high-fiber DASH] vs 6.5 mg/L [supplemented]; P>.05) in obese hypertensive participants. Neither age nor race influenced the response of CRP levels to the diets. No evidence of a crossover effect was detected.

CONCLUSIONS: The results demonstrate that fiber intake of about 30 g/d) from a diet naturally rich in fiber or from a supplement can reduce levels of CRP. Further research is needed to more clearly elucidate the differential effect seen in lean vs obese individuals and whether modification of dietary fiber may be helpful in modulating inflammation and its consequent cardiovascular consequences.

*C-Reactive Protein is a member of the class of acute phase reactants as its levels rise dramatically during inflammatory processes occurring in the body.

+Research Abstract: Cereal fiber intake may reduce risk of gastric adenocarcinomas

Research Abstract: Cereal fiber intake may reduce risk of gastric adenocarcinomas: the EPIC-EURGAST study
M A M, Pera G, Agudo A, Bueno-de-Mesquita HB, Palli D, Boeing H, Carneiro F, Berrino F, Sacerdote C, Tumino R, Panico S, Berglund G, Manjer J, Johansson I, Stenling R, Martinez C, Dorronsoro M, Barricarte A, Tormo MJ, Quiros JR, Allen N, Key TJ, Bingham S, Linseisen J, Kaaks R, Overvad K, Jensen M, Olsen A, Tjønneland A, Peeters PH, Numans ME, Ocké MC, Clavel-Chapelon F, Boutron-Ruault MC, Trichopoulou A, Lund E, Slimani N, Jenab M, Ferrari P, Riboli E, González CA.Int J Cancer. 2007 Oct 1;121(7):1618-23.

Numerous case-control studies suggest dietary fiber may reduce risk of gastric cancer, but this has not been confirmed prospectively. A previous case-control study reported reduced risk of gastric cardia adenocarcinomas associated with cereal fiber, but not with fruit or vegetable fiber. To date, different food sources of fiber have not been examined with respect to noncardia tumors or diverse histologic sub-types. This study prospectively examines associations between fiber from different food sources and incident gastric adenocarcinomas (GC) among more than 435,000 subjects from 10 countries participating in the European Prospective Investigation into Cancer and Nutrition study. Subjects aged 25-70 years completed dietary questionnaires in 1992-98, and were followed up for a median of 6.7 years. About 312 incident GCs were observed. The relative risk of GC was estimated based on cohort-wide sex-specific fiber intake quartiles using proportional hazards models to estimate hazards ratios (HRs) and 95% confidence intervals (CIs). Intakes of cereal fiber, but not total, fruit or vegetable fiber, were associated with reduced GC risk [adjusted HR for the highest vs. lowest quartile of cereal fiber 0.69, 0.48-0.99]. There was a strong inverse association for diffuse [HR 0.43, 0.22-0.86], but not intestinal type [HR 0.98, 0.54-1.80] tumors. Associations for cardia vs. noncardia tumors were similar to those for overall GC, although cardia associations did not reach significance. Cereal fiber consumption may help to reduce risk of GC, particularly diffuse type tumors. Further study on different food sources of fiber in relation to GC risk is warranted to confirm these relationships.

+Research Article: Dietary fibre and risk of breast cancer in the UK Women’s Cohort Study

Dietary fibre and risk of breast cancer in the UK Women’s Cohort Study
Janet Elizabeth Cade, Victoria Jane Burley, Darren Charles Greenwood and the UK Women’s Cohort Study Steering Group

Background

Reports of relationships between dietary fibre intake and breast cancer have been inconsistent. Previous cohort studies have been limited by a narrow range of intakes.

Methods

Women who developed invasive breast cancer, 350 post-menopausally and 257 pre-menopausally, during 240 959 person-years of follow-up in the UK Women’s Cohort Study (UKWCS) were studied. This cohort has 35,792 subjects with a wide range of exposure to dietary fibre with intakes of total fibre in the lowest quintile of <20 g/day up to >30 g/day in the top quintile. Fibre and breast cancer relationships were explored using Cox regression modeling adjusted for measurement error. Effects of fibre, adjusting for confounders were examined for pre- and post-menopausal women separately.

Results

In pre-menopausal, but not post-menopausal women a statistically significant inverse relationship was found between total fibre intake and risk of breast cancer (P for trend=0.01). The top quintile of fibre intake was associated with a hazard ratio of 0.48 [95% confidence interval (CI) 0.24–0.96] compared with the lowest quintile. Pre-menopausally, fibre from cereals was inversely associated with risk of breast cancer (P for trend=0.05) and fibre from fruit had a borderline inverse relationship (P for trend=0.09). A further model including dietary folate strengthened the significance of the inverse relationship between total fibre and pre-menopausal breast cancer.

Conclusions

These findings suggest that in pre-menopausal women, total fibre is protective against breast cancer; in particular, fibre from cereals and possibly fruit.

Introduction

Evidence linking breast cancer to the intake of dietary fibre has been conflicting.1-3 However, the possibility remains that a high dietary fibre intake may be protective. Fibre or certain fibre fractions have been hypothesized to reduce cancer risk through a number of mechanisms4 including inhibition of oestrogen reabsorption, inhibition of human oestrogen synthetase leading to a reduction in oestrogen synthesis and reduction in levels of androgens which influence levels of oestrogens and proliferation of breast tissue.5 Additionally, fibre may act via a route involving insulin and insulin-like growth factors (IGFs). Higher serum levels of IGF-1 are associated with increased breast cancer risk6 and IGF levels are influenced by diet.7

Results from case-control studies have tended to show a protective effect of fibre.2 This study design is more prone to recall bias, and hence cohort studies are potentially more reliable. However, prospective studies which have explored the relationship between dietary fibre intake and breast cancer have not shown a protective effect.8-9 A review of nine prospective studies has shown that risk for breast cancer increases significantly with increasing concentrations of both oestrogens and androgens.10 These sex hormones have been shown to be altered by diets high in fibre in some experimental studies.11-13

The UK Women’s Cohort Study (UKWCS) is well placed to explore the risks of breast cancer associated with dietary fibre and sources of fibre since the Cohort was designed to have a wide range of relevant exposures through inclusion of large numbers of vegetarians.14

Subjects and methods

The UK Women’s Cohort was constructed to have large numbers of subjects in three main groups: vegetarian, eating fish (not meat) and meat eaters. This ensured adequate power for important comparisons involving fruit, vegetables or fish intake as well as associated nutrients including fibre in order to explore potential relationships between diet and cancer whilst minimizing the effects of measurement error.15-17

Baseline data were collected on 35,792 women between 1995 and 1998 via a postal questionnaire to each subject. Women were aged 35-69 years at baseline and were living in England, Wales and Scotland. Women were chosen from ~500,000 responders to a direct mail questionnaire which included general questions on diet. This had been sent by the World Cancer Research Fund to people living in England, Wales and Scotland using direct mail lists targeted towards females, with an overall response rate of 17%. All women in the correct age group and who characterized themselves as vegetarian or non-red meat eaters were invited to take part. A comparison group was selected from the remaining eligible women by selecting, for each vegetarian, the next non-vegetarian in the list aged within 10 years of the vegetarian. Additional detail about the cohort is provided elsewhere.14

Study population

In total, 17,781 women who were post-menopausal at baseline and 15,951 women who were classified as pre-menopausal at baseline were included in this analysis. Menopausal status was coded using specific criteria. Post-menopausal women were those with age at the baseline greater than age at the last period, or if older than 50 years and currently on hormone replacement therapy (HRT), or with a previous hysterectomy and HRT, or if all the above were missing and the woman was >50 years. Pre-menopausal women were those who reported having natural menstrual periods, or were pregnant, or were on HRT and aged 50< years at baseline, or aged <50 years with a previous hysterectomy, or if all the above were missing and the woman was aged <50 years.

Case definition and ascertainment

All subjects were flagged for deaths and cancer registrations on the Office of National Statistics National Health Service central register which was the only source of case information. All malignant breast cancers registered after the subjects returned their questionnaire were taken as newly incident cancers. Cases contributed person-time from date of enrolment until time of diagnosis. Non-cases contributed person-time from date of enrolment until death (807 women) or end of follow-up (January 31, 2004) whichever was the first. In total, 350 post-menopausal and 257 pre-menopausal women developed invasive breast cancer during 240,959 person-years of follow-up. The mean length of follow-up of all non-breast cancer subjects was 7.5 years (range 0.1-9.4).

Dietary data

The self-administered questionnaire consisted of a detailed assessment of diet using a 217-item food frequency questionnaire (FFQ) based on that used in the Oxford arm of the European Prospective Investigation into Cancer (EPIC) study and developed for use with vegetarians. The FFQ has been validated on a subsample of 303 UK Women’s Cohort subjects. Nutrient values from the FFQ were compared with values from a 4-day food diary and also fasting blood measures of specific nutrients.18

This study examined amounts of dietary fibre in grams per day calculated by multiplying the frequency of consumption of each food by the nutrient content of the indicated portion size and summing overall foods. Nutrient composition of foods was taken from UK food composition tables19; Englyst fibre values were used in this report. Dietary fibre fractions were assessed by estimating the fibre consumption derived from the relevant foods or food groups.

Statistical methods

The relationship between fibre and breast cancer was explored using Cox’s proportional hazards regression using Stata version 9.1.20 Associations were estimated for pre-and post-menopausal women separately, first as a simple model adjusting for age and total energy intake, second as a full model adjusting for age, body mass index (BMI), physical activity (hours/day sufficiently vigorous to cause sweating), current smoking status, oral contraceptive use, HRT use, number of children, alcohol consumption and total energy intake at baseline. To take account of the stratified sampling scheme in the analysis, in all models, individuals were weighted by the inverse of the probability of being sampled. Sensitivity analyses were carried out (i) excluding women who were diagnosed with breast cancer within 1 year of completing the FFQ, (ii) excluding individuals with any previous malignant cancer and (iii) with further adjustment for dietary folate in light of concerns regarding the confounding effect of folate on dietary fibre.10,21

A second FFQ was taken from a sample of 1918 (5%) of the cohort from which the amount of random measurement error was estimated using a regression calibration approach22,23 to obtain individual predicted values of dietary exposure for all participants. Cox’s proportional hazards regression was then run using the predicted values for each individual categorized into quintiles to give estimated hazard ratios (HRs) corrected for some of the effects of measurement error. The 95% confidence intervals (CIs) were obtained from bootstrapped estimates.24

Results

The mean (SD) age of the cohort subjects was 52 (9) years at baseline, 44.8 (4.5) years for pre-menopausal women and 58.8 (7.5) years for post-menopausal women. The majority of the women were white (99%), married (75%) with children (86%) and middle class (63% National Statistics-Socio Economic Class 1— Professional and Managerial class25). The cohort were well educated (27% had a degree) and over half were currently in employment. The mean (SD) BMI of the women was 24.5 (4.3) kg/m2. Only 11% of the cohort were current smokers. Further details of the cohort have been reported elsewhere.14

Cohort food and nutrient characteristics

Eighteen per cent (6224) of the women were vegetarian based on meat eating frequency from the FFQ, 12% (3961) were fish eaters and 70% (23,547) meat eaters. The mean energy intake was 2361 kcal (median 2261 kcal) with 32%, 53% and 15% of energy provided by fat, carbohydrate and protein, respectively. Mean (SD) dietary fibre intake was high at 26 (11) g/day, and was highest amongst the fish eaters at 29 (11) g/day compared with vegetarians 28 (11) g/day and meat eaters 24 (10) g/day. Vitamin and mineral intakes from the diet, excluding supplements, were also high as illustrated by the mean vitamin C intake (172 mg, median 156 mg). Further nutrients are presented in Table 1.

In post-menopausal women, nutrient intakes did not differ greatly between those with and without breast cancer. Premenopausal women with breast cancer had a higher percentage of energy derived from protein and also lower total carbohydrate, sugar, dietary fibre (Englyst) and vitamin C compared with cancer-free women. Only the difference in percentage energy from protein was statistically significant in this univariable analysis.

Table 1: Mean (SD) nutrient intakes for total sample and by breast cancer status

		Pre-menopausal women		Post-menopausal women
	Total sample	Breast cancer n = 257	Non-breast cancer n = 15,694	Breast cancer n = 350	Non-breast cancer n = 17,431

Calories including alcohol	2361 (801)	2322 (710)	2358 (710)	2300 (657)	2336 (719)
Protein (g)	90 (32)	88 (26)	87 (27)	91 (28)	91 (28)
Energy from protein(%)	15.1 (2.5)	15.0 (2.7)	14.7 (2.4)	15.6 (2.5)	15.4 (2.6)
Carbohydrate (g)	315 (113)	307 (104)	313 (103)	307 (97)	313 (106)
Energy from carbohydrate(%)	52.6 (7.0)	52.2 (6.8)	52.5 (6.8)	52.7 (7.3)	52.8 (7.1)
Sugars (g)	148 (60)	141 (65)	145 (58)	151 (57)	152 (62)
Starch (g)	157 (59)	157 (58)	160 (59)	149 (57)	153 (59)
Fat (g)	85 (36)	84 (32)	86 (32)	82 (29)	84 (32)
Energy from fat(%)	32.4 (5.8)	32.7 (5.6)	32.7 (5.8)	32.0 (5.8)	32.2 (5.8)
Fibre (Englyst) (g)	26 (11)	25 (11)	25 (10)	25 (9)	26 (11)
Vitamin C (mg)	172 (92)	159 (72)	166 (84)	178 (81)	175 (88)
Folate (µg)	404 (146)	390 (126)	395 (131)	399 (119)	407 (138)
Vitamin A (µg)	1249 (633)	1184 (592)	1173 (547)	1314 (620)	1300 (633)
Iron (mg)	18.9 (8.1)	18.2 (7.1)	18.5 (7.3)	18.7 (6.8)	19.1 (8.0)
Calcium (mg)	1141 (411)	1120 (409)	1129 (378)	1133 (366)	1144 (382)
Zinc (mg)	11.5 (4.3)	11.2 (3.5)	11.2 (3.7)	11.8 (3.8)	11.7 (3.9)

Fibre models

In the basic multivariable analysis, total fibre intake in premenopausal women was inversely related to risk of breast cancer. In the more complex model, the strength of association increased showing an inverse relationship of total fibre intake with risk of breast cancer (P for trend=0.01) (Table 2).

Exploring the sources of fibre showed that in pre-menopausal women, fibre from cereals was inversely associated with risk of breast cancer (P for trend=0.05) and fibre from fruit had a borderline non-significant inverse association (P for trend=0.09) (Table 2). There were no significant relationships between breast cancer and total fibre or fibre from cereals, fruit or vegetables in post-menopausal women.

Results from the sensitivity analysis after excluding women diagnosed within a year of completing the FFQ were not appreciably altered. Excluding all women with any malignant cancer prior to the study commencing did not alter the conclusions either. Including dietary folate as a potential confounder in addition to the other variables in the original complex model strengthened the significance of the inverse relationship between total fibre and pre-menopausal breast cancer (HR comparing top with bottom quintile 0.33; 95% CI 0.14–0.79; P for trend=0.003).

Table 2: Relative risks of pre- and post-menopausal breast cancer according to quintiles of fibre intakes and fibre fractions in the UK Women's Cohort

	Basic modela				Complex modelb
	Cases/ non-cases	Person-years	Hazard Ratio	95% CI	Cases/ non-cases	Person-years	Hazard Ratio	95% CI

Pre-menopausal women
Total fibre quintiles (range, g)
Quintile 1 (<20)	51/3136	23,154	1	–	47/2851	21,066	1	–
Quintile 2 (20,23)	56/3131	23,161	1.16	0.75–1.81	54/2845	21,083	1.14	0.72–1.81
Quintile 3 (23,26)	66/3122	23,375	1.18	0.78–1.80	60/2838	21,231	1.05	0.64–1.72
Quintile 4 (26,30)	40/3147	23,582	0.63	0.36–1.08	35/2864	21,456	0.63	0.34–1.17
Quintile 5 (30+)	44/3144	23,881	0.61	0.34–1.10	36/2863	21,753	0.48	0.24–0.96
Trend				P = 0.03				P = 0.01
Cereal fibre quintiles (range, g)
Quintile 1 (<4)	55/3132	23,137	1	–	54/2844	21,049	1	–
Quintile 2 (4,7)	53/3134	23,288	1.02	0.68–1.53	51/2848	21,155	1.06	0.72–1.58
Quintile 3 (7,9)	54/3134	23,395	0.84	0.51–1.37	45/2853	21,309	0.73	0.46–1.15
Quintile 4 (9,13)	47/3140	23,589	0.83	0.52–1.33	40/2859	21,476	0.68	0.42–1.09
Quintile 5 (13+)	48/3140	23,744	0.68	0.35–1.33	42/2857	21,599	0.59	0.32–1.10
Trend I				P = 0.20				P = 0.05
Fruit fibre quintiles (range, g)
Quintile 1 (<2)	51/3136	23,181	1	–	48/2850	21,083	1	–
Quintile 2 (2,3)	68/3119	23,297	1.42	0.96–2.12	64/2835	21,191	1.36	0.89–2.06
Quintile 3 (3,4)	51/3137	23,385	0.97	0.62–1.52	43/2855	21,278	0.81	0.50–1.32
Quintile 4 (4,6)	39/3148	23,527	0.60	0.38–0.97	36/2863	21,408	0.61	0.36–1.04
Quintile 5 (6+)	48/3140	23,762	0.89	0.55–1.42	41/2858	21,628	0.81	0.44–1.49
Trend				P = 0.24				P = 0.09
Vegetable fibre quintiles (range, g)
Quintile 1 (<3)	42/3145	23,450	1	–	40/2858	21,316	1	–
Quintile 2 (3,4)	66/3121	23,272	1.57	1.03–2.38	57/2842	21,201	1.45	0.93–2.26
Quintile 3 (4,5)	47/3141	23,360	1.23	0.76–2.00	44/2854	21,223	1.15	0.73–1.82
Quintile 4 (5,7)	58/3129	23,432	1.61	1.02–2.53	52/2847	21,318	1.62	0.99–2.65
Quintile 5 (7+)	44/3144	23,639	1.32	0.77–2.24	39/2860	21,530	1.26	0.73–2.18
Trend				P = 0.78				P = 0.96
Post-menopausal women
Total fibre quintiles (range, g)
Quintile 1 (<21)	61/3489	24,149	1	–	52/3018	20,950	1	–
Quintile 2 (21,23)	73/3477	24,420	1.40	1.02–1.91	60/3011	21,213	1.40	0.96–2.03
Quintile 3 (23,26)	78/3473	24,637	1.31	0.92–1.88	65/3005	21,348	1.49	1.00–2.24
Quintile 4 (26,30)	79/3471	24,845	1.31	0.94–1.84	63/3008	21,541	1.34	0.87–2.07
Quintile 5 (30+)	59/3492	25,501	1.14	0.72–1.81	46/3025	22,128	1.18	0.70–1.99
Trend				P = 0.70				P = 0.97
Cereal fibre quintiles (range, g)
Quintile 1 (<4)	60/3490	24,273	1	–	48/3022	21,074	1	–
Quintile 2 (4,7)	79/3471	24,469	1.36	0.94–1.97	69/3002	21,232	1.50	1.05–2.16
Quintile 3 (7,9)	76/3475	24,662	1.35	0.92–1.99	66/3004	21,347	1.53	1.03–2.29
Quintile 4 (9,13)	71/3479	24,897	1.31	0.92–1.88	54/3017	21,611	1.25	0.81–1.93
Quintile 5 (13+)	64/3487	25,251	1.23	0.77–1.95	49/3022	21,916	1.15	0.68–1.94
Trend				P = 0.96				P = 0.89
Fruit fibre quintiles (range, g)
Quintile 1 (<2)	57/3493	24,252	1	–	50/3020	21,042	1	–
Quintile 2 (2,3)	70/3480	24,477	1.15	0.79–1.67	60/3011	21,233	1.17	0.79–1.72
Quintile 3 (3,5)	80/3471	24,656	1.46	1.04–2.05	65/3005	21,367	1.47	1.00–2.16
Quintile 4 (5,7)	78/3472	24,877	1.33	0.94–1.87	59/3012	21,599	1.22	0.80–1.86
Quintile 5 (7+)	65/3486	25,289	1.17	0.75–1.84	52/3019	21,939	1.10	0.66–1.84
Trend				P = 0.58				P = 0.64
Vegetable fibre quintiles (range, g)
Quintile 1 (<3)	68/3482	24,403	1	–	56/3014	21,165	1	–
Quintile 2 (3,4)	62/3488	24,655	0.90	0.63–1.29	48/3023	21,424	0.86	0.57–1.29
Quintile 3 (4,6)	75/3476	24,640	1.22	0.85–1.76	64/3006	21,362	1.32	0.87–2.01
Quintile 4 (6,8)	75/3475	24,760	1.23	0.85–1.79	61/3010	21,464	1.27	0.85–1.92
Quintile 5 (8+)	70/3481	25,094	1.21	0.82–1.77	57/3014	21,766	1.20	0.74–1.94
Trend				P = 0.69				P = 0.40

All types of fibre corrected for measurement error. ^aAdjusted for age and total energy intake corrected for measurement error. ^bAdjusted for age, BMI, physical activity, current smoking status, oral contraceptive use, hormone replacement therapy use, number of children, alcohol intake, total energy intake corrected for measurement error.

Discussion

The most important finding was that in this cohort, total fibre intake was protective against breast cancer in pre-menopausal women. This effect was not seen in the post-menopausal women. Exploring the sources of dietary fibre showed that cereal fibre is protective against breast cancer pre-menopausally and that fruit fibre, although not statistically significant, was potentially protective.

The mean FFQ derived fibre intake in the UKWCS was 26 g/day which is markedly higher than that reported in a national survey of UK adults using the food diary technique.26 In the UKWCS, more than 80% of women eat more fibre than the national average of 12 g/day. The women tend to consume more fruits and vegetables than an average person in the UK. Although this mean is high, it is similar to intakes observed in other cohort studies using FFQ-based dietary assessments.14,27 The EPIC Oxford cohort found that women who were meat eaters had a fibre intake of 19 g/day and women who were vegetarians ate 22 g fibre/day.28

This is the first large prospective study to show a relationship between total fibre intake and risk of pre-menopausal breast cancer. Previous analysis from the Canadian National Breast Screening Study did not find any relationship between fibre or fibre fractions and breast cancer risk, however, that study combined pre- and post-menopausal status.9 The Nurses Health Study also reported no relationship between fibre or fibre fractions and risk of breast cancer, a specific analysis of 714 cases of pre-menopausal breast cancer did not find a strong association with fibre intake.29 That cohort may have been too homogeneous with respect to fibre intake since only 0.7% consumed as much as 30 g fibre/day whereas 28% of the UKWCS consumed at least 30 g fibre/day. However, in that cohort there was a suggestion of reduced risk when comparing those who ate >30 g fibre/day with those eating <10 g/day (HR 0.68; 95% CI 0.43-1.06).8 A number of case-control studies have shown inverse associations with dietary fibre and risk of breast cancer30-33 for both pre- and post-menopausal women.

Our results are particularly informative because they also show that fibre from cereals and potentially also from fruit may be the important sources of fibre resulting in this inverse relationship with breast cancer pre-menopausally. Epidemiological studies exploring intakes of fruits and vegetables and risk of breast cancer have shown conflicting results. A meta-analysis of 26 cohort and case-control studies found no association with fruit and breast cancer risk although there was an inverse relationship with vegetable consumption.1 A pooled analysis of eight cohorts found no significant relationship between fruit or vegetable intakes and risk of breast cancer.34 However, the amounts and specific types of fruits and vegetables consumed may influence results obtained. A case-control study from France has shown that cereal fibre is protective against breast cancer with an odds ratio (OR) of 0.56 (95% CI 0.31-1.03) comparing the top (>5.6 g/day) with the bottom quintile (=3 g/day) of intake and with a significant test for trend (P=0.03).30,33 Our cohort had a much wider range of intakes of cereal fibre than in that study.

Our assessment of total fibre used the Englyst values for non-starch polysaccharides from the UK composition of foods database.19 This includes only the polysaccharide components of cell walls and as such tends to produce somewhat lower values than the other common method for assessing dietary fibre which is based on the weight of residual matter following enzymic treatment of food.35 However, for fruit and vegetable fibre, the estimates do not differ greatly. The Association of Official Analytical Chemists (AOAC) method may overestimate at the lower end of the scale, but the Englyst method may underestimate at the upper end of the scale, since lignans are not included.36 Non-starch polysaccharides are the most abundant components of plant cell walls and have been considered to have protective properties. It may be that other aspects of a high fibre diet are important such as the combination of micronutrients including antioxidant vitamins and glycaemic index.8 However, when we included folate in our complex model as an additional confounder the strength of the association with fibre was increased. Studies which have explored the risk of colon cancer in relation to dietary fibre have been inconsistent in their findings and this has been ascribed, at least in part, to the lack of adjustment for dietary folate consumption which has been positively correlated with dietary fibre intake.37

As well as allowing exploration of higher fibre intakes, the wide range of dietary intakes that our study was designed to include reduces the impact of measurement error.15-17 In the presence of measurement error, which occurs in every dietary assessment study, selecting a population with larger exposure variance compared with one with smaller variance allows the study sample size to be reduced by a factor equal to the ratio of the smaller to larger variance.17 We further corrected for bias from the random component of measurement error in the FFQ through use of a replicate FFQ measure. However, this does not correct for other components of measurement error and may represent incomplete correction for measurement error bias. Other studies have shown that using food diaries may result in even stronger estimates.38 No biomarkers exist for fibre intake with which to calibrate FFQs or food diaries.

Our analysis adjusted for most of the major lifestyle factors which could act as confounders of the relationship between dietary fibre and breast cancer. It could be that adjustment for other factors such as use of dietary supplements or family history of breast cancer would have been informative. We had information on the use of any dietary supplements and also whether the subjects’ parents had ever suffered from cancer or heart disease. Inclusion of these variables as proxies in further sensitivity analyses did not affect the overall results. Residual confounding due to incomplete adjustment from unmeasured or poorly measured confounders is still a possibility.

Although we could not find any other cohort studies of fibre and breast cancer risk which had reported results for pre- and post-menopausal women which differed in the same way as our results, one case-control study by McCann et al.33,39 found that pre-menopausal women in the highest quartile of dietary lignan intake had reduced breast cancer risk (OR 0.66; 95% CI 0.44-0.98) whereas no association was observed between lignan intakes and post-menopausal breast cancer. Particularly rich sources of lignans are seeds and whole grains which are also good sources of fibre.

Interestingly, we did not observe a protective effect of fibre intake post-menopausally. The oestrogen metabolism pathway differs between pre- and post-menopausal women.40 The endocrine basis of premenopausal breast cancer is not clear. Hyperandrogenism with luteal inadequacy could induce breast cancer or alternatively excess oestrogen plus progesterone, particularly during the luteal phase may be involved.41 Elevated blood concentrations of androgens have been associated with an increased risk of breast cancer in premenopausal women in a nested case-control analysis from the European Prospective Investigation into Cancer study.5 Diets high in fibre and low in fat have been shown to affect sex hormone levels.5,42,43 Two small studies which supplemented women with wheat bran showed differing results. Premenopausal women who were supplemented with 10 or 20 g wheat bran/day for 2 months found a significant reduction in oestradiol concentrations44 whereas a study of post-menopausal women found no effect of supplementation with wheat bran on oestradiol, androstenedione or sex hormone-binding globulin.45 A high fibre or vegetarian diet also influences cycle length in pre-menopausal women which is linked to oestrogen exposure, but clearly does not have this effect in post-menopausal women.46

Other mechanisms, such as a route through glucose metabolism, may be involved. Glucose is a key substrate for neoplastic cell proliferation and insulin is a powerful mitogenic agent. Associations of breast cancer risk with glucose, insulin and IGF-I pattern for post-menopausal women were generally weaker than for pre-menopausal women and not statistically significant in a nested case-control study from Italy.47 It is possible that other factors such as body size or weight gain from early adult life to after the menopause may have an overriding impact on sex hormone levels post-menopausally and that this could explain why the protective effect was only seen pre-menopausally. Weight gain has been consistently shown to be related to increased risk of post-menopausal breast cancer.4,48-51 Adult weight gain reflects body fat content. Oestrogens derived from aromatization of androstenedione in peripheral fat may account for the increased risk of breast cancer observed among post-menopausal obese women.33 Weight gain post-menopausally may outweigh any other dietary effects. Genes which pre-dispose to earlier breast cancer may work through influencing hormone concentrations, which can also be modified by diet.52-53 Alternatively, the relevant dietary exposure may be earlier in life, so pre-menopausal women are closer to the relevant time window and hence less subject to the effect of measurement error bias.

In summary, dietary fibre has a protective effect against pre-menopausal breast cancer in this cohort. This was not seen for women who were post-menopausal. The specific food sources of this dietary fibre which had a protective effect pre-menopausally were cereals and possibly fruit.

Contributors

J.E.C. initiated and developed the cohort and made a primary contribution to the analysis and writing of the report. V.J.B. managed the cohort and was responsible for quality control of all procedures and contributed to the data analysis. D.C.G. has been the cohort statistician and undertook the analysis and made a primary contribution to writing the report. The Steering Group had oversight of the conduct of the cohort.

Steering Group

Rhys Williams (Chair), Professor of Clinical Epidemiology, University of Wales, Swansea.
Barrie Margetts, Nutritional Epidemiologist, University of Southampton.
David Forman, Professor of Cancer Epidemiology, University of Leeds.
Jenny Barrett, Genetic Epidemiologist, University of Leeds.
Margaret Thorogood, Professor of Epidemiology, University of Warwick.

Acknowledgements

The UKWCS was funded by the World Cancer Research Fund. Thanks to James Thomas for database management, Claire Calvert and Alyson Greenhalgh for previous cohort support, Helene Tribodet for work on an earlier analysis of cohort data and all the nutrition students who have supported this project.

Conflict of interest: The Nutritional Epidemiology Group has received some funding for research and consultancy from the Kelloggs Company.

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