Dietary fiber: Essential for a healthy diet

Fiber provides many health benefits. Here's how to fit more into your diet.

By Mayo Clinic staff

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 foods containing fiber can provide other health benefits as well, such as helping to maintain a healthy weight and lowering your risk of diabetes and heart disease.

Selecting tasty foods that provide fiber isn't difficult. Find out how much dietary fiber you need, the foods that contain it, and how to add them to meals and snacks.

What is dietary fiber?

Dietary fiber, also known as roughage or bulk, includes all parts of plant foods that your body can't digest or absorb. Unlike other food components, such as fats, proteins or carbohydrates — which your body breaks down and absorbs — fiber isn't digested by your body. Instead, it passes relatively intact through your stomach, small intestine, colon and out of your body.

Fiber is commonly classified as soluble (it dissolves in water) or insoluble (it doesn't dissolve):

  • Soluble fiber. This type of fiber dissolves in water to form a gel-like material. It can help lower blood cholesterol and glucose levels. Soluble fiber is found in oats, peas, beans, apples, citrus fruits, carrots, barley and psyllium.
  • Insoluble fiber. This type of fiber promotes the movement of material through your digestive system and increases stool bulk, so it can be of benefit to those who struggle with constipation or irregular stools. Whole-wheat flour, wheat bran, nuts, beans and vegetables, such as cauliflower, green beans and potatoes, are good sources of insoluble fiber.

Most plant-based foods, such as oatmeal and beans, contain both soluble and insoluble fiber. However, the amount of each type varies in different plant foods. To receive the greatest health benefit, eat a wide variety of high-fiber foods.

Benefits of a high-fiber diet

A high-fiber diet has many benefits, which include:

  • Normalizes bowel movements. Dietary fiber increases the weight and size of your stool and softens it. A bulky stool is easier to pass, decreasing your chance of constipation. If you have loose, watery stools, fiber may also help to solidify the stool because it absorbs water and adds bulk to stool.
  • Helps maintain bowel health. A high-fiber diet may lower your risk of developing hemorrhoids and small pouches in your colon (diverticular disease). Some fiber is fermented in the colon. Researchers are looking at how this may play a role in preventing diseases of the colon.
  • Lowers cholesterol levels. Soluble fiber found in beans, oats, flaxseed and oat bran may help lower total blood cholesterol levels by lowering low-density lipoprotein, or "bad," cholesterol levels. Studies also have shown that fiber may have other heart-health benefits, such as reducing blood pressure and inflammation.
  • Helps control blood sugar levels. In people with diabetes, fiber — particularly soluble fiber — can slow the absorption of sugar and help improve blood sugar levels. A healthy diet that includes insoluble fiber may also reduce the risk of developing type 2 diabetes.
  • Aids in achieving healthy weight. High-fiber foods generally require more chewing time, which gives your body time to register when you're no longer hungry, so you're less likely to overeat. Also, a high-fiber diet tends to make a meal feel larger and linger longer, so you stay full for a greater amount of time. And high-fiber diets also tend to be less "energy dense," which means they have fewer calories for the same volume of food.

Another benefit attributed to dietary fiber is prevention of colorectal cancer. However, the evidence that fiber reduces colorectal cancer is mixed.

How much fiber do you need?

How much fiber do you need each day? The Institute of Medicine, which provides science-based advice on matters of medicine and health, gives the following daily recommendations for adults:

 Age 50 or youngerAge 51 or older
Men 38 grams 30 grams
Women 25 grams 21 grams

Institute of Medicine, 2012

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References
  1. Park Y, et al. Dietary fiber intake and risk of colorectal cancer. JAMA. 2005;294:2849.
  2. Dietary Reference Intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids (macronutrients). Institute of Medicine. http://www.nap.edu/openbook.php?isbn=0309085373. Accessed Aug. 22, 2012.
  3. Marshall JR. Nutrition and colon cancer prevention. Current Opinion in Clinical Nutrition & Metabolic Care. 2009;12:539.
  4. Duyff RL. American Dietetic Association Complete Food and Nutrition Guide. 4th ed. Hoboken, N.J.: John Wiley & Sons; 2012:55.
  5. Slavin JL. Position of the American Dietetic Association: Health implications of dietary fiber. Journal of the American Dietetic Association. 2008;108:1716.
  6. Nelson JK (expert opinion). Mayo Clinic, Rochester, Minn. Aug. 22, 2012.
  7. Schatzkin A, et al. Dietary fiber and whole-grain consumption in relation to colorectal cancer in the NIH-AARP Diet and Health Study. American of the Journal Clinical Nutrition. 2007;85:1353.
  8. Dietary Guidelines for Americans, 2010. U.S. Department of Health and Human Services. http://www.cnpp.usda.gov/DGAs2010-PolicyDocument.htm. Accessed Aug. 22, 2012.
  9. Wald A. Management of chronic constipation in adults. http://www.uptodate.com/index. Accessed Aug. 21, 2012.
NU00033 Nov. 17, 2012

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