Fiber

Dietary fiber is part of every plant food. Although it is most often a carbohydrate, dietary fiber is calorie free in humans because we don’t possess the enzymes to break it down.

Many different components in plant foods are categorized as dietary fibers, and not all fiber is the same. One way of grouping fiber is by how easily it dissolves in water in the body.

Soluble fiber partially dissolves in water, forming a jelly-like bulk in the stomach and in the small intestine that’s associated with fullness, lower blood cholesterol levels and lower blood glucose concentrations. Oatmeal, oat bran, apples, citrus fruits, legumes, and psyllium (a plant product used in common over-the-counter fiber and laxative supplements) are particularly rich in soluble fiber.

Several scientific studies have found a link between soluble fiber intake and a lower cholesterol level in the blood. Elevated blood cholesterol levels are a risk factor for heart disease. The U.S. Food and Drug Administration (FDA) allows a health claim like the following on the labels of food products that contain a minimum of .75 grams per serving of soluble fiber from whole oats: “Soluble fiber from foods such as oat bran, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.”

As the name implies, insoluble fiber does not dissolve in water. Insoluble fibers add bulk in the colon and help the body retain water, resulting in softer and larger stools that pass faster, helping to prevent constipation. Whole grains, bran, nuts, and vegetables are especially good sources of insoluble fiber.

The differences between soluble and insoluble fiber are important when it comes to dietary fiber’s effect on your health, but not when considering how much fiber to eat every day. Expert recommendations for daily fiber intake do not specify how much of each type of fiber to eat. Every plant food contains a mixture of soluble and insoluble fiber, so a high-fiber diet provides healthy amounts of both types. *

Relevant Health Areas

How much do I need?
 
Recommended Dietary Allowance
Tolerable Upper Intake Level
 
 
 
IU - International Units
Values determined by the Institute of Medicine (IOM)
 
Suggested Supplements
Best Bets
Also Supports
fruits Suggested Foods
 
 
 
 

Good source of

If you suddenly and significantly increase fiber intake, you may experience some gas, cramping, and bloating, but those effects don’t typically last as your body becomes more accustomed to a higher fiber intake. Gradually increase fiber-rich foods or supplements in your diet and drink plenty of fluids.

Psyllium may reduce the absorption of certain prescription and over-the-counter medications. Ask your doctor or pharmacist about how psyllium, and other fiber supplements, affect the medications you take on a regular basis.

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

  2. United States Department of Agriculture. Agricultural Research Serving. Nutrient Data Laboratory. http://www.ars.usda.gov/main/site_main.htm?modecode=12-35-45-00.

  3. Natural Standard. Bottom Line Monograph. High Fiber Diet. http://naturalstandard.com/databases/hw/generic-highfiberdiet.asp

  4. Linus Pauling Institute. Micronutrient Information Center. Fiber. http://lpi.oregonstate.edu/infocenter/phytochemicals/fiber/

  5. United States Department of Agriculture, Center for Nutrition Policy and Promotion. Dietary Guidelines for Americans, 2010. http://www.cnpp.usda.gov/DGAs2010-PolicyDocument.htm

Foods that are naturally rich in fiber, such as legumes, whole grains, fruits, and vegetables, also supply many other nutrients, including digestible carbohydrates your body uses for energy, vitamins, minerals, and phytonutrients, which are protective plant compounds. That’s why it’s important to reach suggested dietary fiber goals with food first. Unfortunately, most Americans don’t consume enough fiber, thus making it a nutrient of public health concern according to the USDA’s 2010 dietary guidelines for Americans.

Many over-the-counter fiber supplements contain psyllium, which is made from the husks of psyllium seeds. Psyllium is a soluble fiber. The FDA (Food and Drug Administration) has approved health claims like the following on the labels of foods containing at least 1.7 grams per serving of soluble fiber from psyllium: “Diets low in saturated fat and cholesterol that include seven grams a day of soluble fiber from psyllium may reduce the risk of heart disease. Psyllium is also helpful for treating constipation. You can maximize the stool-softening effect of psyllium by drinking plenty of fluid.”

Other commonly available forms of fiber supplements include inulin, wheat dextrin, guar gum, calcium polycarbophil and methylcellulose.

+ Have a nutrition question?  Answers From WebMD