fiber, dietary

What can high-fiber foods do for you?

• Support bowel regularity
• Help maintain normal cholesterol levels
• Help maintain normal blood sugar levels
• Help keep unwanted pounds off

What events can indicate a need for more high fiber foods?

• Constipation
• Hemorrhoids if related to straining from constipation
• High blood sugar levels
• High cholesterol levels

Excellent food sources of fiber include: turnip greens, mustard greens, cauliflower, collard greens, broccoli, Swiss chard, and raspberries.

For serving size for specific foods, see Nutrient Rating Chart below at the bottom of this page.

Description Function Deficiency Symptoms Toxicity Symptoms Cooking, storage and processing Factors that affect function

Drug-nutrient interaction Nutrient interaction Health conditions Supplements Food Sources Public Recommendations References

Description

What is dietary fiber?

Dietary fiber 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.

Although 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, 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

How it Functions

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 play 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 acid 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.

In addition, fermentable fibers 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).

Deficiency Symptoms

What are deficiency symptoms for dietary fiber?

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.

Toxicity Symptoms

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.

Impact of Cooking, Storage and Processing

How do cooking, storage, or processing affect dietary fiber?

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.

Factors that Affect Function

What factors might contribute to a deficiency of dietary fiber?

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.

Drug-Nutrient Interactions

What medications affect dietary fiber?

• Dietary fiber, especially the fiber found in fruit, beans, and oat bran, reduces the absorption of a class of cholesterol-lowering medications called HMG-CoA reductase inhibitors (for example, lovastatin) by binding to the drug in the gastrointestinal tract.
• Dietary fiber decreases the absorption of hydralazine, digoxin, and lithium.
• Diets high in dietary fiber may improve glucose control in people with type 2 diabetes, thereby reducing the dose of insulin or oral glucose lowering medications needed to control blood sugar.
• Certain medications, including pain medications (for example, codeine) and calcium channel blockers (for example, verapamil) can cause constipation.
• Increased intake of dietary fiber can reduce the constipation caused by these medications.

Nutrient Interactions

How do other nutrients interact with dietary fiber?

Foods high in nonfermentable fiber, or the fiber that passes all the way through the intestines unchanged, may reduce the absorption and/or increase the excretion of several minerals, including calcium and iron.

Health Conditions

What health conditions require special emphasis on dietary fiber?

A diet high in fiber may play a role in the prevention and/or treatment of the following health conditions:

• Breast cancer
• Cardiovascular disease
• Colon cancer
• Constipation
• Diabetes
• Diverticulitis
• Gallstones
• High cholesterol
• Irritable bowel syndrome
• Obesity
• Syndrome X

Form in Dietary Supplements

What forms of dietary fiber are found in dietary supplements?

As a dietary supplement and over-the-counter medication, fiber is available in powders that can be mixed with water or juice. These products often contain psyllium as the source of fiber, but may also contain pectin or guar gum. In addition, oat bran is available as a fiber-rich food ingredient that can be added to baked goods or hot cereal.

Food Sources

What foods provide dietary fiber?

Excellent food sources of dietary fiber include: turnip greens, mustard greens, cauliflower, collard greens, broccoli, Swiss chrd and raspberries.

Very good sources of dietary fiber include romaine lettuce, celery, spinach, fennel, green beans, eggplant, cranberries, strawberries and flax seeds.

Good sources of dietary fiber include cucumber, apricots, navy beans, grapefruit, rye, sweet potato, beets, buckwheat, shiitake mushrooms and oats.

 

Introduction to Nutrient Rating System Chart

In order to better help you identify foods that feature a high concentration of nutrients for the calories they contain, we created a Food Rating System. This system allows us to highlight the foods that are especially rich in particular nutrients. The following chart shows the World's Healthiest Foods that are either an excellent, very good, or good source of dietary fiber. Next to each food name, you'll find the serving size we used to calculate the food's nutrient composition, the calories contained in the serving, the amount of dietary fiber contained in one serving size of the food, the percent Daily Value (DV%) that this amount represents, the nutrient density that we calculated for this food and nutrient, and the rating we established in our rating system. For most of our nutrient ratings, we adopted the government standards for food labeling that are found in the U.S. Food and Drug Administration's "Reference Values for Nutrition Labeling." Read more background information and details of our rating system.

World's Healthiest Foods ranked as quality sources of: dietary fiber
Food	Serving Size	Cals	Amount (g)	DV (%)	Nutrient Density	World's 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
Garbanzo 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 each	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
Spelt grains, cooked	4 oz-wt	144.0	4.40	17.6	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
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
Oats, whole grain, cooked	1 cup	147.4	3.98	15.9	1.9	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%

Public Health Recommendations

What are current public health recommendations for dietary fiber?

In its most recent 2005 public health recommendations for fiber (published as the Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients), National Academies Press, 2005), the National Academy of Sciences established an Adequate Intake (AI) level of 38 grams of total daily fiber for males 19-50 years of age and 25 grams for women in this same age range. It also noted that individuals in this age range in the United States only get about half this much fiber each day.

References

• American Association of Cereal Chemists. The definition of dietary fiber. Cereal Foods World 2001; 46(3), 112-127 2001.
• American Dietetic Association. Health implications of dietary fiber - - Position of the ADA. Journal of the American Dietetic Association 1997; 97:1157-1159 1997.
• Burton-Freeman B. Dietary fiber and energy regulation. J Nutr 2000 Feb;130(2S Suppl):272S-5S 2000. PMID:15360.
• Cohen LA. Dietary fiber and breast cancer. Anticancer Res 1999 Sep-1999 Oct 31;19(5A):3685-8 1999. PMID:15370.
• Davy BM and Melby CL. The effect of fiber-rich carbohydrates on features of Syndrome X. J Am Diet Assoc 2003 Jan;103(1):86-96 2003.
• Fernandez ML. Soluble fiber and nondigestible carbohydrate effects on plasma lipids and cardiovascular risk. Curr Opin Lipidol 2001 Feb;12(1):35-40 2001.
• Flamm G, Glinsmann W, Kritchevsky D, et al. Inulin and oligofructose as dietary fiber: a review of the evidence. Crit Rev Food Sci Nutr 2001 Jul;41(5):353-62 2001. PMID:15310.
• Garcia Peris P, Camblor Alvarez M. [Dietary fiber: concept, classification and current indications]. Nutr Hosp 1999 May;14 Suppl 2:22S-31S 1999. PMID:15380.
• Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995 1995.
• Institute of Medicine. Dietary Reference Intakes: Proposed Definition of Dietary Fiber. National Academy Press, Washington DC, 2001 2001.
• Lininger SW, et al. A-Z guide to drug-herb-vitamin interactions. Prima Health, Rocklin, CA, 2000 2000.
• Mahan K, Escott-Stump S. Krause's Food, Nutrition, and Diet Therapy. WB Saunders Company; Philadelphia, 1996 1996.
• McIntosh M, Miller C. A diet containing food rich in soluble and insoluble fiber improves glycemic control and reduces hyperlipidemia among patients with type 2 diabetes mellitus. Nutr Rev 2001 Feb;59(2):52-5 2001.
• Meseguer Soler I, Martinez Para MC, Farre Rovira R. [Dietary fiber (and II). Metabolism and physiologic implications]. Med Clin (Barc) 1998 Jan 17;110(1):32-7 1998. PMID:15390.
• Pereira MA, Ludwig DS. Dietary fiber and body-weight regulation. Observations and mechanisms. Pediatr Clin North Am 2001 Aug;48(4):969-80 2001. PMID:15320.
• Pereira MA, Pins JJ. Dietary fiber and cardiovascular disease: experimental and epidemiologic advances. Curr Atheroscler Rep 2000 Nov;2(6):494-502 2000. PMID:15350.
• Swanson KS, Fahey GC. New developments in the area of dietary fiber. Nutrition in Complementary Care Newsletter 2001; 4(1):5,12 2001.
• Zhao X, Yang Y, Song Z et al. Effect of superior fiber complex on insulin sensitivity index and blood lipids in non-insulin dependent diabetes mellitus rats. Zhonghua Yu Fang Yi Xue Za Zhi 2002 May;36(3):184-6 2002.

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