The old adage “An apple a day keeps the doctor away” is beginning to make scientific sense. Dietary fiber is fast becoming recognized as an important protective component of our diet.
Most of the so-called “diseases of affluence” are associated with diets low in fiber. The long list includes constipation, hemorrhoids, diverticulitis, gallstones, appendicitis, varicose veins, bowel cancer, obesity, diabetes and even heart disease.
Fiber in the diet could well influence the risk of heart disease because of its effects on blood cholesterol levels, obesity and diabetes.
What is Fiber?
Dietary fiber or “roughage” is generally regarded as the parts of plant food that cannot be entirely digested. However, bacteria normally present in the intestines can break down much of the fiber. The term “fiber” is now taken to include the many different components of the structural parts of the stem, leaves, fruit and seeds.
Fiber’s main function is to create a bulk in the intestines to help carry away waste material. It does this by absorbing many times its own weight of water. A soft bulk is created which mixes with other food wastes, and is then sped through the gut. It is when dietary fiber is lacking that constipation and associated problems arise.
Obesity is rarely found among populations eating high fiber diets. Fiber can help to control obesity in several ways. Fiber foods, such as potatoes, vegetables and fruit contain few calories for their large volume.
Not only are such foods bulk-forming and filling, but the extra chewing required before swallowing tends to lessen the amount of food eaten. For example, one large, fresh apple would fill most people, yet the juice from two or three apples is quickly swallowed without chewing and is not filling.
Furthermore, when fiber foods replace foods with a high fat or sugar content there is a significant saving in calories. Indeed, one study showed that men, given 10 large potatoes to eat each day, and being allowed whatever other food they fancied, were able to lose weight because they didn’t want much else.
Additionally, fiber can physically interfere with the complete digestion and absorption of fats and other nutrients in the intestines. This small wastage of energy could be significant over a period in helping to control weight.
Fiber and Diabetes
Despite the traditional treatment of diabetes with a low-carbohydrate diet, recent research indicates that a high carbohydrate diet containing naturally occurring carbohydrate food gives better long-term control. Blood sugar levels do not rise excessively when the meal contains fiber foods rather than refined carbohydrates; and insulin requirements are lowered.
Fiber and Cholesterol
Each day more than 50 percent of the cholesterol made in the body is converted into bile salts to aid digestion and absorption of fats from food eaten. Most bile salts are reabsorbed into the body for further use.
However, certain types of fiber – such as that found in soy beans, chickpeas, lentils and spinach – are capable of binding bile salts in the intestines and excreting them. If this happens, more cholesterol is broken down in the liver to replenish the supply of bile salts. Blood cholesterol levels may subsequently become moderately lowered.