Dietary Fiber

I

Introduction

Dietary Fiber, the undigestable part of plants consumed as food. It is sometimes called bulk or roughage and is found in fruits, vegetables, and grains. Dietary fiber consists primarily of cellulose, a component of plant cell walls. Because fiber cannot be digested, nutritionists disregarded it for many years. But since the 1970s researchers have better understood the health benefits of fiber, and it is now considered an important part of a healthy diet. See also Human Nutrition.

II

Types of Fiber

Nutritionists classify fiber into two types. Soluble fiber dissolves in water; nonsoluble fiber does not dissolve in water. The two types have different effects on the body.

When soluble fiber mixes with water, it forms a gel-like substance that slows digestion and helps the intestines absorb valuable nutrients from food. Nonsoluble fiber passes through the small intestine largely unchanged. In the large intestine, it softens and adds bulk to the stool (solid body wastes) and helps food pass through more quickly. Both types of fiber have health benefits.

III

Health Benefits of Fiber

Dietary fiber increases the body’s sense of fullness. Therefore, diets high in fiber can help prevent overeating and obesity. High-fiber foods also tend to have fewer calories for their volume than foods lower in fiber—another plus for dieters.

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A diet high in fiber protects against constipation. Constipation and straining to move the bowels can increase pressure on the intestinal wall and lead to other conditions such as hemorrhoids and diverticulitis. Diets low in fiber increase the risk of developing these conditions.

Fiber also appears to have an effect on heart disease and diabetes. Studies have shown that soluble fiber lowers levels of artery-clogging cholesterol in the bloodstream. High cholesterol levels can contribute to arteriosclerosis and coronary heart disease. Fiber can also slow the body’s absorption of sugar. By lowering glucose (blood sugar) levels, fiber can help people with type II diabetes.

For a time dietary fiber was thought to offer some protection against colorectal cancer by dissolving and removing cancer-causing substances from the large intestine. A link between fiber consumption and colorectal cancer was found in small studies. However, larger studies failed to confirm that finding.

IV

Sources of Fiber

Most people in industrialized societies consume too little dietary fiber. People can boost their intake of dietary fiber by eating more fruits, vegetables, and grains. Dried peas and beans are especially high in fiber. Whole-grain breads have more fiber than white bread or pasta. Raw and cooked fruits and vegetables have more fiber than juices and other processed fruits and vegetables. Bran muffins, oatmeal, brown rice, and multiple-grain cereals are all high in fiber. So is popcorn, but skip the butter.

People who increase their consumption of fiber should also drink more liquids to avoid constipation. In addition, it is a good idea to add fiber to the diet slowly. Eating more fiber over a short period can cause bloating, intestinal gas (see Flatulence), and mild abdominal cramping. These symptoms usually disappear as intestinal bacteria adjust to the increase in fiber.

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