Consuming Dietary Fiber

Dietary fiber comes from the portion of plants that is not digested by enzymes in the intestinal tract. Part of it, however, may be metabolized by bacteria in the lower gut.

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 but do nothing to increase fecal bulk. Beans, oat bran, fruit and vegetables contain soluble fiber.

In contrast, fibers in cell walls are water insoluble. These include cellulose, hemicellulose and lignin. Such fibers increase fecal bulk and 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.

Sometimes there is confusion as to the difference between crude fiber and dietary fiber. Both are determined by a laboratory analysis, but crude fiber is only one-seventh to one-half of total dietary fiber.

Benefits of Fiber

Insoluble fiber binds water, making stools softer and bulkier. Therefore, 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. However, more recent studies have not confirmed the protective effects of fiber in developing colon cancer. 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. Likewise, whole wheat bread contains more fiber than white bread.

Disorders connected with a lack of dietary fibre

The most obvious effect of dietary fibre is on stool bulk.

.Constipation
Constipation is a significant problem in communities where fibre intake is low, but is virtually unknown when the diet is high in fibre.

•Haemorrhoids
Haemorrhoids are common and occur at any age un peoples of all races, both sexes and all occupations. There is also a direct association between haemorrhoids and a highly-refined low fibre diet. This causes constipation, that leads to straining at stool. Increasing the fibre content of the diet will prevent constipation and relieve the symptoms of haemorrhoids.

•Irritable bowel syndrome
Increasing dietary fibre and using a bulking agent may be the only treatment needed for Irritable Bowel Syndrome.

•Diverticular Disease
Diverticular disease is unknown in rural Africans who eat a high-fibre diet, but is common in Western societies where many people have a low fibre intake. It is much less common in vegetarians.

•Bowel cancer
The cause of bowel cancer is unknown but there is good evidence that dietary and other environmental factors promote it, at least in genetically-susceptible individuals.

•Diabetes
People with type 2 diabetes benefit from an increase in dietary fibre and resistant starch. A high fibre diet is also likely to be low in fat and this is a further advantage.

•Raised Blood Cholesterol
Some soluble fibre found in oats, psyllium and barley, and also the pectin from certain fruits , can reduce blood cholesterol. Foods high in soluble fibre have benefits for those with high levels of cholesterol in blood, but a diet low in saturated fat is even more important.

Although fiber is important, it is just one part of a properly balanced diet. It is possible that too much fiber may reduce the amount of calcium, iron, zinc, copper and magnesium that is absorbed from foods. Deficiencies of these nutrients could result if the amount of fiber in the diet is excessive, especially in young children.

Fiber supplements are sold in a variety of forms from bran tablets to purified cellulose. Many laxatives sold as stool softeners actually are fiber supplements. Fiber's role in the diet is still being investigated. It appears that the various types of fiber have different roles in the body. Furthermore, fiber may interact wil prescription medications.

For these reasons, avoid fiber supplements. Instead, eat a variety of fiber-rich foods. This is the best way to receive the maximum benefits from each type of fiber present in foods, and obtain necessary nutrients.