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
  • 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.

 

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 psyllium seed husk, is known to promote bowel regularity. Despite the widespread use of these terms 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.

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

Introduction to Nutrient Rating System Chart

The following chart shows the foods which are either excellent, very good or good sources of this nutrient. Next to each food name you will find the following information: the serving size of the food; the number of calories in one serving; DV% (percent daily value) of the nutrient contained in one serving (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. For more detailed information on our Nutrient Rating System, please click here.

 

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
Greens, Turnip, Cooked 1 cup 28.8 5.04 20.2 12.6 excellent
Basil, 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, Ground 2 tsp 9.2 1.28 5.1 10.1 very good
Raspberries, Fresh 1 cup 60.3 8.34 33.4 10.0 excellent
Thyme, Ground 2 tsp 7.9 1.08 4.3 9.8 good
Greens, Mustard, 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
Lettuce, Romaine 2 cup 15.7 1.90 7.6 8.7 very good
Cauliflower (boiled, drained) 1 cup 28.5 3.35 13.4 8.5 excellent
Peppermint Leaves, Fresh 1 oz-wt 19.9 2.27 9.1 8.2 very good
Collard Greens, Boiled, Drained 1 cup 49.4 5.32 21.3 7.8 excellent
Broccoli (pieces, steamed) 1 cup 43.7 4.68 18.7 7.7 excellent
Cloves, 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
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, with salt) 1 cup 41.4 4.32 17.3 7.5 very good
Chili Peppers, Red, Dried 2 tsp 25.5 2.64 10.6 7.5 very good
Pepper, Black 2 tsp 10.9 1.12 4.5 7.4 good
Fennel Bulb, Sliced, Raw 1 cup 27.0 2.70 10.8 7.2 very good
Parsley, Fresh 1 oz-wt 10.2 0.94 3.8 6.6 good
Green Snap/String Beans, Boiled 1 cup 43.8 4.00 16.0 6.6 very good
Eggplant, Boiled 1 cup 27.7 2.48 9.9 6.4 very good
Pepper, Cayenne, Dried 2 tsp 11.2 0.96 3.8 6.2 good
Cranberries, raw, whole 0.50 cup 23.3 1.99 8.0 6.2 very good
Strawberries, Fresh 1 cup 43.2 3.31 13.2 5.5 very good
Red Bell Peppers (sliced, raw) 1 cup 24.8 1.84 7.4 5.3 very good
Squash, Winter, All Varieties 1 cup 80.0 5.74 23.0 5.2 very good
Kale, Fresh, Boiled 1 cup 36.4 2.60 10.4 5.1 very good
Split Peas, Boiled 1 cup 231.3 16.27 65.1 5.1 very good
Squash, Summer, All Varieties 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
Dill Seed 2 tsp 13.4 0.93 3.7 5.0 good
Lentils, Boiled 1 cup 229.7 15.64 62.6 4.9 very good
Brussels 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
Beans, Black, Boiled 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
Beans, Pinto, Cooked 1 cup 234.3 14.71 58.8 4.5 very good
Cucumber, Raw 1 cup 13.5 0.83 3.3 4.4 good
Beans, Lima, Cooked 1 cup 216.2 13.16 52.6 4.4 very good
Turmeric, Ground 2 tsp 16.0 0.96 3.8 4.3 good
Seeds, Flax 0.25 cup 190.6 10.80 43.2 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, Red, Raw, 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
Beans, Kidney, Cooked 1 cup 224.8 11.33 45.3 3.6 very good
Barley 1 cup 270.0 13.60 54.4 3.6 very good
Apricots, Raw 1 each 16.8 0.84 3.4 3.6 good
Blueberries, Fresh 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
Beans, Garbanzo, 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
Beets, Boiled 1 cup 74.8 3.40 13.6 3.3 good
Beans, Navy, Cooked 1 cup 258.4 11.65 46.6 3.2 good
Grapefruit 0.50 each 60.0 2.70 10.8 3.2 good
Figs, Fresh 8 oz-wt 167.8 7.48 29.9 3.2 good
Pear, Bartlett 1 each 97.9 3.98 15.9 2.9 good
Rye Cereal, Cream of, Cooked 1 cup 108.6 4.32 17.3 2.9 good
Soybeans, Cooked 1 cup 297.6 10.32 41.3 2.5 good
Yam, Dioscorea species, Cubes, Cooked 1 cup 157.8 5.30 21.2 2.4 good
Sweet Potato (small, baked with skin) 1 each 95.4 3.14 12.6 2.4 good
Avocado, All Varieties 1 cup 235.1 7.30 29.2 2.2 good
Seeds, Mustard 2 tsp 35.0 1.08 4.3 2.2 good
Prunes, Dried 0.25 cup 101.6 3.02 12.1 2.1 good
Buckwheat Groats, Cooked 1 cup 154.6 4.54 18.2 2.1 good
Mushrooms, Shiitake, Raw 8 oz-wt 87.2 2.49 10.0 2.1 good
Olives, Ripe 1 cup 154.6 4.30 17.2 2.0 good
Oats, Whole Grain 1 cup 145.1 3.98 15.9 2.0 good
Plum 1 each 36.3 0.99 4.0 2.0 good
Mushrooms, Crimini, Raw 5 oz-wt 31.2 0.85 3.4 2.0 good
Miso (Soybean) 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, Boiled 1 cup 177.1 4.60 18.4 1.9 good
Pineapple 1 cup 76.0 1.86 7.4 1.8 good
Cantaloupe 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
Seeds, Sesame 0.25 cup 206.3 4.24 17.0 1.5 good
Almonds 0.25 cup 205.2 4.19 16.8 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?

No official Recommended Dietary Allowance for dietary fiber has been established by the Institute of Medicine at the National Academy of Sciences. However, various health and nutrition organizations have issued recommendations for dietary fiber intake.

For example, the American Dietetic Association, the American Diabetes Association, and the National Cancer Institute encourage a minimum intake of 25 grams of dietary fiber per day.

References

  • American Association of Cereal Chemists. The definition of dietary fiber. Cereal Foods World 2001; 46(3), 112-127.
  • American Dietetic Association. Health implications of dietary fiber - - Position of the ADA. Journal of the American Dietetic Association 1997; 97:1157-1159.
  • Burton-Freeman B. Dietary fiber and energy regulation. J Nutr 2000 Feb;130(2S Suppl):272S-5S.
  • Cohen LA. Dietary fiber and breast cancer. Anticancer Res 1999 Sep-1999 Oct 31;19(5A):3685-8.
  • 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.
  • Fernandez ML. Soluble fiber and nondigestible carbohydrate effects on plasma lipids and cardiovascular risk. Curr Opin Lipidol 2001 Feb;12(1):35-40.
  • 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.
  • Garcia Peris P, Camblor Alvarez M. [Dietary fiber: concept, classification and current indications]. Nutr Hosp 1999 May;14 Suppl 2:22S-31S.
  • Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995.
  • Institute of Medicine. Dietary Reference Intakes: Proposed Definition of Dietary Fiber. National Academy Press, Washington DC, 2001.
  • Lininger SW, et al. A-Z guide to drug-herb-vitamin interactions. Prima Health, Rocklin, CA, 2000.
  • Mahan K, Escott-Stump S. Krause's Food, Nutrition, and Diet Therapy. WB Saunders Company; Philadelphia, 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.
  • 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.
  • Pereira MA, Ludwig DS. Dietary fiber and body-weight regulation. Observations and mechanisms. Pediatr Clin North Am 2001 Aug;48(4):969-80.
  • Pereira MA, Pins JJ. Dietary fiber and cardiovascular disease: experimental and epidemiologic advances. Curr Atheroscler Rep 2000 Nov;2(6):494-502.
  • Swanson KS, Fahey GC. New developments in the area of dietary fiber. Nutrition in Complementary Care Newsletter 2001; 4(1):5,12.
  • 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.

This page was updated on: 2004-11-21 11:11:56
© 2002 The George Mateljan Foundation