Can high‑fiber diets really do all they claim to do? Studies have examined the relationship between high‑fiber diets and many diseases, including colon cancer, coronary heart disease and diabetes. Proven benefits of a high‑fiber diet include prevention and treatment of constipation, hemorrhoids and diverticulosis. In addition, certain types of fiber help decrease blood cholesterol levels.
Dietary fiber comes from the portion of plants that is not digested by enzymes in the intestinal tract. The body cannot completely break down fiber for use as an energy source. Roughage is another name for fiber. Fiber is in the supporting structure of plants’ leaves, stems, fruits and seeds.
Different types of plants have varying amounts and kinds of fiber, including pectin, gum, mucilage, cellulose, hemicellulose and lignin. Pectin and gum are water‑soluble fibers found inside plant cells. They slow the passage of food through the intestines. Beans, oat bran, fruit and vegetables contain soluble fiber.
In contrast, fibers in cell walls are water insoluble. These include cellulose, hemicellulose and lignin. These fibers speed up the passage of food through the digestive tract. Wheat bran and whole grains contain the most insoluble fiber, but vegetables and beans also are good sources.
Fiber, especially that found in whole grain products, is helpful in the treatment and prevention of constipation, hemorrhoids and diverticulosis. Diverticula are pouches of the intestinal wall that can become inflamed and painful. In the past, a low‑fiber diet was prescribed for this condition. It is now known that a high‑fiber diet gives better results once the inflammation has subsided.
Low blood cholesterol levels (below 200 mg/dl.) have been associated with a reduced risk of coronary heart disease. The body eliminates cholesterol through the excretion of bile acids. Water‑soluble fiber binds bile acids, suggesting that a high‑fiber diet may result in an increased excretion of cholesterol. Some types of fiber, however, appear to have a greater effect than others. The fiber found in rolled oats is more effective in lowering blood cholesterol levels than the fiber found in wheat. Pectin has a similar effect in that it, too, can lower the amount of cholesterol in the blood.
Other claims for fiber are less well founded. Dietary fiber may help reduce the risk of some cancers, especially colon cancer. This idea is based on information that insoluble fiber increases the rate at which wastes are removed from the body. This means the body may have less exposure to toxic substances produced during digestion. A diet high in animal fat and protein also may play a role in the development of colon cancer.
High‑fiber diets may be useful for people who wish to lose weight. Fiber itself has no calories, yet provides a “full” feeling because of its water‑absorbing ability. For example, an apple is more filling than a half cup of apple juice that contains about the same calories. Foods high in fiber often require more chewing, so a person is unable to eat a large number of calories in a short amount of time.
Sources of fiber
Dietary fiber is found only in plant foods: fruits, vegetables, nuts and grains. Meat, milk and eggs do not contain fiber. The form of food may or may not affect its fiber content. Canned and frozen fruits and vegetables contain just as much fiber as raw ones. Other types of processing, though, may reduce fiber content. Drying and crushing, for example, destroy the water‑holding qualities of fiber.
The removal of seeds, peels or hulls also reduces fiber content. Whole tomatoes have more fiber than peeled tomatoes, which have more than tomato juice. Also, whole wheat bread contains more fiber than white bread.
How much fiber?
The current recommendations for fiber is 25 to 35 grams per day. However, the average American only consumes 14 grams of dietary fiber per day.
For many people, meeting the recommended intake for fiber may require changes in their eating habits. Eating several servings of whole grains, fruits, vegetables and dried beans each day is good way to boost fiber intake. However, if you are not used to eating high fiber foods regularly, these changes should be made gradually to avoid problems with bloating, gas and diarrhea. Be sure to drink plenty of liquids as you increase your fiber. Anyone with a chronic disease should consult a physician before greatly altering a diet.
Source: Colorado Cooperative Extension, North Carolina Cooperative Extension
Sandra R. Cain is the Bladen County Extension director. She can be reached by email at [email protected]