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The Complete Guide to Fiber


Fiber is essential for short-term and long-term health. It helps control weight, aids digestion, lowers the risk of hemorrhoids, and helps regulate blood sugar levels. 


It's also thought to play a role in the treatment and/or prevention of diabetes, heart disease (it lowers cholesterol levels), and diverticulosis (small pouches in the lining of the colon). There is some evidence that dietary fiber lowers the risk of colorectal cancer, but the research is inconclusive.

Fiber by the Numbers

The average amount of fiber (in grams) Americans eat each day

The amount of fiber (in grams) children, adolescents and adults should eat every day

The number of fiber (in grams) an adult should consume for every 1,000 calories eaten. The Institute of Medicine recommends men 50 years and younger should get 38 grams of fiber daily, while women need 25 grams. Men 51 and over need 30 grams a day and women should have 21 grams.

How Fiber Works

Soluble fiber—the kind that dissolves in water and turns into a gel-like substance—slows the digestive process. When a water-soluble source, such as oatmeal, mixes with water, the gel substance formed helps to slow the emptying of stomach waste into the small intestine. This may prolong satiety and promote weight loss. The gel also latches onto the cholesterol in the diet and excretes it as waste with the stool which can effectively lower blood cholesterol levels for healthier heart function.

Insoluble fiber—the kind that doesn’t dissolve in water—helps to move food through the digestive system and increases the bulk in stool. This characteristic is the key to a healthy digestive system. As the bulk moves through the intestinal tract, it pushes against the intestinal walls, which causes the walls to “push back.” This pushing expedites the passage of waste through the intestines and acts as a “workout” for the digestive system.

As the waste continues to move through, it tones the muscles of the intestinal walls and prepares for the exit of healthy, bulky stool. Without this intestinal workout, waste can’t move through the intestines with ease. This causes constipation that could lead to hemorrhage or inflammation. That is why it benefits those who suffer from chronic constipation or irregular bowel movements.

Sources of Fiber

Dietary fiber comes from grains, vegetables and fruits. Soluble fiber is contained in oats, peas, beans, apples, citrus fruits, carrots, strawberries and barley. Insoluble fiber comes in whole-wheat flour, wheat bran, rye, cabbage, turnips, apple skin, nuts and many vegetables.

Supplemental forms can be sprinkled on meals to improve their nutritional value. Below are examples of high-fiber foods and their content in grams provided by the United States Department of Agriculture.

Food Serving Size Fiber Content (grams)
Split peas 1 cup 16.3
Red kidney beans 1 cup 13.1
Raspberries 1 cup 8.0
Whole-wheat spaghetti 1 cup 6.3
Oat bran muffin Medium 5.2
Pear 1 medium-size 5.1
Broccoli 1 cup 5.1
Apple 1 medium-size 4.4
Oatmeal 1 cup 4.0
Green beans 1 cup 4.0
Brown rice 1 cup 3.5
Popcorn 2 cups 2.3
Whole-wheat bread 1 slice 1.9

Too Much of a Good Thing?

  • Eating too much fiber in a short period of time can cause stomach cramps, bloating and gas.
  • Too much fiber can interfere with the absorption of minerals, but most high-fiber foods are rich in minerals.
  • If you decide to add fiber to your diet, do it gradually to reduce the likelihood of gas and diarrhea.
  • Fiber supplements (Metamucil, Citrucel, Fibercon) seem to be effective, but there is little research to support that claim. High-fiber foods are better because they contain vitamins, minerals and other nutrients. Fiber One contains 14 grams of fiber—exactly the amount recommended earlier for every 1,000 calories consumed and more than half needed by most people on a daily basis.
  • Peeling fruits and vegetables can reduce the amount of fiber.
  • Commercial oat bran and wheat bran muffins, chips and waffles tend to be high in total fat, saturated fat and sodium.

Take-Home Message

Fiber is the workhorse of the digestive tract and a food type that should not be ignored. Consuming a high-fiber diet can help improve day-to-day waste management, assist in an efficient metabolism for energy maintenance, and promote an overall improvement of health and well-being. Promising research is showing that fiber not only does the dirty work of digestion, but that it may be very important in preventing and treating a variety of diseases and conditions.

Tags: Food, Carbohydrate, Nutrients, Metabolism


  1. American Dietetic Association
  2. American Heart Association
  3. Institute of Medicine
  4. MayoClinic.com
  5. Medline Plus
  6. National Digestive Diseases Information Clearinghouse
  7. United States Department of Agriculture