High-Fiber Diet

Grandma called it roughage, today we call it fiber. Fiber has become a household word and high fiber foods are being promoted in many grocery stores. However, interest in fiber is not a recent development. Hippocrates, the Father of Medicine, recommended making bread from whole grain flour for its "beneficial effect on the bowels." Fiber will not cure or prevent all diseases, but it should be a part of a healthy diet.

Fiber is a part of the cell wall in every plant. It holds the plant together. Most fibers are carbohydrates. Our bodies cannot digest them. Thus the fiber portion of the food does not contribute calories to the diet. Fiber is found only in plants; the tough fibrous parts of meat are not considered dietary fiber.

There are different types of fiber in your diet—cellulose, hemicellulose, pectin, gums and lignin. Different plants have different types of fiber. The fiber in oats for example, is different from the fiber in celery. The amount of fiber varies from one kind of plant to another and may vary within a species or variety. Whole-wheat bread, apples and cabbage each contribute fiber to the diet, but the benefit of each will be different because they have different types of fiber. By eating a variety of whole grains, cereals, fruits, vegetables and legumes, you can incorporate all the different types of fiber into your diet.

The functions of fiber vary with the type of fiber. Cellulose, hemicellulose, and lignin are water-insoluble fibers. The gums and pectins are water-soluble fibers. The insoluble types act like sponges, holding water and cleaning your intestines as they pass through. This cleaning action may prevent cancer-causing substances from remaining in the intestine long enough to cause cancer. The increased amount of water in the feces produces softer, larger stools. Softer stools are more easily eliminated, which can help prevent constipation.

Softer stools may also help in preventing the formation of diverticula (small pockets in the small intestine) that can collect waste material and become infected. Foods containing the water-insoluble types of fiber may also be helpful in treating diverticulosis—the condition when many diverticula are present. High fiber diets may help prevent diverticulitis—infection in the diverticula.

An important function of the water-soluble fibers, in oats, beans, peas and fruit, is lowering blood cholesterol, thereby decreasing your risk of heart disease. These same fibers may also help control blood sugar (glucose) by slowing down the rate of food leaving the stomach. This could be helpful in the treatment of diabetes.

Our knowledge of fiber is far from complete, but we do know that all the benefits do not come from one type of fiber. Therefore adding fiber in the form of bran or cellulose alone may not provide the total benefits of fiber. It's best to get a variety of fibers from a variety of foods high in fiber.

Here's a chart of some fiber types, where they're found, and what they do.

How Much Fiber?

During the past century, the fiber content of the diet has substantially declined. The "refining" of many food products further decreases the fiber value of the food. It is estimated that the average American gets only 19 grams of fiber a day. Many researchers suggest you should eat at least 25 grams of fiber a day.

Increasing fiber intake of the diet can benefit you, but if too much is added too quickly, it can create problems. The most common problem of overloading on fiber is intestinal gas. Although this is not a health problem, it can be inconvenient. In severe cases, the intestinal gas produced by too much fiber may be accompanied by bloating, stomach pains or diarrhea. Increase fiber gradually into the diet to give your digestive tract time to adapt to the additional load.

A more serious problem created by too much fiber is the possible loss of some trace minerals like zinc, calcium, iron and magnesium. Some types of fiber bind to these minerals and prevent them from being absorbed. When large amounts of fiber are added to diets high in fats and sweets, nutrient deficiencies may develop. No problems should occur with the gradual addition of a moderate amount (about 25 gm) of fiber to a well-balanced diet. The addition of fiber to the diet should not lead to the exclusion of other nutritious foods. Fiber is just one part of a balanced diet.

The fiber content of foods listed in food composition tables may be expressed as crude fiber or dietary fiber. The dietary fiber content of foods is the one you should look for. Crude fiber is only the indigestible cellulose and lignin portions of grains, fruits and vegetables. It is the portion of the food that remains after it is chemically treated with strong acid and alkali. Dietary fiber refers to the combined fiber in food. Because dietary fiber values include cellulose and lignin as well as the other types of fiber, it provides a more accurate assessment of the fiber content of the diet. Laboratory methods to measure dietary fiber values in all foods are still being established. The dietary fiber values for a limited number of foods have been determined, but as the research in this area progresses, these values may change.

Dietary Fiber of Selected Foods

	Fruit
			SERVING SIZE		GRAMS OF DIETARY FIBER
	Apple, with skin		1		3.0
	Banana		1		1.8
	Orange		1		3.6
	Peach		1		1.4
	Pear		1		4.3
	Prunes		3		1.9
	Raisins		2 Tbs.		1.1
	Strawberries		3/4 cup		2.9
	Vegetables
			SERVING SIZE		GRAMS OF DIETARY FIBER
	beans, baked		1/2 cup		9.7
	Black-eyed peas		1/2 cup		8.3
	Broccoli, cooked		1/2 cup		2.0
	Cabbage, raw		1/2 cup		0.8
	Carrots, raw		1		2.3
	Potato, baked, no skin		1		2.3
	Potato, baked, with skin		1		4.1
	Winter squash		1/2 cup		2.8
	Cereal Products
			SERVING SIZE		GRAMS OF DIETARY FIBER
	Bran flakes		1/2 cup		9.1
	Oatmeal, cooked		1/2 cup		2.0
	Oat bran		1 oz. cooked		4.4
	Whole wheat bread		1 slice		2.0

Labels Can Be Confusing

Fiber is a popular word, and it appears prominently on many bread and cereal labels. Some labels do not, however, tell how much fiber is present or how beneficial it is. If you are trying to get more fiber from baked products, start by looking for baked products labeled "whole wheat." These products must contain only whole wheat flour (also called graham flour). While products labeled "wheat bread" often look like whole wheat bread, they are usually made of mixtures of white and whole wheat flours, and they contain less fiber than whole wheat bread. Check the list of ingredients to see what you're buying. Ingredients are listed in decreasing order of the amount present. So if the first or second ingredient is whole wheat flour or another whole grain flour, the bread will provide more fiber than one that lists whole grain flour as the fifth or sixth ingredient.

Adding Fiber to Your Diet

It takes more than "an apple a day" to add fiber to your diet, but it is a start. Fresh fruits make beautiful refreshing desserts or snacks. Adding fruits to your main dish can add flavor and texture as well as fiber. You can keep the fiber in your food through careful food preparation techniques at home. Cooking can break down some types of fibers and may slightly reduce the fiber content of the food. The major loss of fiber, however, is when fruits are peeled, mashed or grated before they're cooked.

Whole grains can add exciting new flavors and textures to your meals and snacks. Whole wheat croutons are good on salads. Try some oatmeal muffins made from regular oatmeal, or make colorful open-faced sandwiches using whole grain breads. Some people are rediscovering the delight of creating their own tasty breads using whole grain flours. Most supermarkets now sell a variety of whole grain breads including whole wheat and mixed grain products. No longer should the bread-basket be limited to plain, white bread.

White bread is not necessarily a nutritional loser. It does have B vitamins, iron and some protein, and one slice contains only about 70 calories. But whole grain breads have the additional benefit of fiber. One slice of whole wheat bread has more than four times as much fiber as one slice of enriched white bread.

Whole wheat bread also contains small amounts of trace minerals not found in enriched white bread. Enrichment replaces the iron and B vitamins lost in the refinement process, but other vitamins and minerals that are lost are not returned to the flour. While these minerals are present in whole grain bread, they may not be totally available to your body because whole grains also contain some substances that partially block the absorption of some trace minerals.

Experiment with dried beans and peas such as pinto beans, lentils and black beans. They are excellent in traditional dishes like red beans and rice and chili. For more of the fiber they offer, try adding them to soups, casseroles or even sandwich spreads. Because of their high protein content, dried beans and peas can be a major part of a meatless meal.

Increasing Fiber During Food Preparation

• Use fresh fruits and vegetables for snacks and deserts.
• Eat the peel on fruits and vegetables.
• Cut fruits or vegetables into chunks for salads, deserts or casseroles instead of grating them.
• Use whole grain rice, noodles and bread products.
• Substitute whole grain flour for 1/4 to 1/2 of the regular all-purpose flour in recipes.
• Mix mashed legumes with ground beef in spicy casseroles or meat loaves.
• Add oatmeal or oat bran to drop cookies, muffins or meat loaves.
• Sprinkle bran on cereal, vegetables, desserts or ice cream.

Reprinted from Alley, H. (1997). Fiber for the Health of It. Athens, Georgia: University of Georgia, Cooperative Extension Service.

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