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Fiber—a Bulk of Benefits
by Don Buscher, MS
Don is a freelance food and health writer based in Asheville, NC. He also analyses recipes for Delicious Magazine.
Many of us may remember our mothers telling us to eat our roughage because it was good for us. As youth, we may have questioned her knowledge and motives, but she was right on. It has long been known that fiber, formally called roughage or bulk, is the safest and most effective way to treat and prevent constipation. However, research done over the past twenty-five years has greatly expanded our understanding of fiber's health benefits. Scientists now recognize that fiber may cut the risk of the leading chronic diseases—heart disease, diabetes, and cancer.
Unfortunately the fiber intake of Americans has steadily declined over the past 60 years. Since the advent of food processing, grain-based foods like bread, cereal, rice, and pasta have been stripped of their fiber- and nutrient-rich bran and germ. Today, whole grains make up a mere 5 percent of the grain foods we eat. Our disproportionate consumption of refined grains may be costing us our health, if not our lives.
So what exactly is dietary fiber?
Dietary fiber isn't a single substance but rather a large group of indigestible compounds found in vegetables, fruits, nuts, grains and legumes. Meats, dairy and eggs do not contain fiber. There are two basic types of fiber—soluble and insoluble. Many foods contain some of both, but the predominate fiber determines the texture of that portion of the food.
How do soluble and insoluble fibers differ?
Soluble fibers such as gums, mucilages, and algal polysaccharides, are chiefly found inside plant cells. They soak up water and thus tend to be viscous and have a gelatinous or gummy texture. They are abundant in oatmeal, oat bran, flax seed, psyllium (seed husks from plantain), fruit pectin, citrus fruits, beans, potatoes, strawberries and apple pulp. Insoluble fibers, on the other hand, include cellulose, hemicellulose and lignin that are components of cell walls. They do not dissolve in water and are found in the tough, chewy parts of plants such as apple skins, vegetable skins, wheat bran, brown rice, and nuts. They are also in bananas, lentils, green beans, peas, and beans.
Soluble fibers can reduce elevated cholesterol levels and lower the risk of hypertension and heart disease. In 1998, the Food and Drug Administration (FDA) approved the health claim "May reduce the risk of heart disease" for foods that contain at least 1.7 grams soluble fiber and meet certain nutritional criteria. They lower cholesterol by binding with bile acids and transporting them out of the body. Because bile acids are made out of cholesterol, the liver pulls cholesterol from the blood to make more.
Soluble fibers also help control the rise in blood sugar following a meal which is particularly important for those with diabetes, and they promote a feeling of fullness that can help with weight control. Insoluble fibers assist the passage of food through the digestive track, thereby preventing constipation and reducing the risk of diverticulitis.
What Studies Have Found
Heart Disease
Most of the research on heart disease done so far has looked at the fiber in whole grains. A study of more than 43,000 male health professionals found that those who reported eating an average of 29 grams of fiber, particularly from whole grains, each day had a 41 percent lower risk of heart attack than those who averaged 12 grams a day (J. Amer. Med. Assoc. 275: 447, 486, 1996).
Likewise, a nine year study at the University of Minnesota involving 30,000 women observed a 30 percent lower risk of dying from heart disease in the women who consumed at least 3 servings of whole grains each day compared to those who averaged less than one serving a day. And a study of 22,000 Finnish men, found that the men who ate approximately 35 grams of fiber a day experienced a 31 percent lower risk of heart attack than those who only averaged 16 grams a day (Circulation 94: 2720, 1996).
This doesn't mean you have to dine exclusively on whole grains. If you prefer white rice or pasta made with refined white flour, then balance that with whole-grain breakfast cereals and breads.
Diabetes
Soluble fiber, especially gums and pectins, appear to delay the emptying of the stomach and slow the absorption of glucose in the intestine. This reduces the need for large amounts of insulin to balance blood sugar levels. Less insulin means a lower glycemic load which in theory should lower the risk of diabetes. The Harvard study of 80,000 nurses found that women with the lowest fiber intake and the highest glycemic load had a two-and-a-half times greater risk of diabetes.
Five grams of psyllium-seed husk taken three times a day significantly reduced blood sugar levels as well as triglycerides, total cholesterol and LDL cholesterol in a double-blind, placebo-controlled study of 125 people with Type II diabetes (published in the Journal of Diabetes Complications , fall of 1998).
Diverticulosis
The National Institutes of Health estimates that 10 percent of Americans over age 40 and 50 percent over age 60 suffer from diverticulosis, a condition where pockets form in the large intestine. This disorder is most prevalent in societies where fiber intake tends to be low. Although 80 percent have no symptoms, food trapped in these pockets can cause abdominal pain, flatulence, constipation, and inflammation (diverticulitis).
According to a study of nearly 48,000 male health professionals, a high-fiber diet may reduce risk of diverticular disease. Those eating 32 grams of fiber a day reported fewer symptoms of diverticulosis than those eating 13 grams of fiber a day (Amer. J. Clin. Nutr. 60: 757,1994). It was once thought that "roughage" was rough on the bowels and that a person with diverticulosis should go on a low-fiber diet; however, that was found to make the condition worse. Fiber provides the bulk needed to move food more efficiently and easily through the intestines.
Cancer
Although a recent large-scale study did not find a high-fiber diet to protect against colon cancer, an extensive epidemiology study published in the November 1998 issue of the Journal of the National Cancer Institute examined data from 59 countries and found that mortality from prostate cancer is inversely associated with consumption of grains and nuts. Other studies show people who eat high-fiber diets have lower risks of cancers of the mouth, throat, esophagus, larynx and stomach.
Fiber-rich foods are a storehouse of nutrients
High-fiber foods—fruits, vegetables, and unrefined grains—tend to be low in fat and calories and high in vitamins, minerals, and phytochemicals that provide additional protection against cancer and other diseases. What's more, some of them contain phytoestrogens—plant hormones that are thought to play a roll in reducing the risk of heart disease and breast cancer.
Although fiber can bind some trace minerals, such as iron, zinc, and magnesium, the effect is minimal, as the rich supply of minerals in high-fiber foods more than offset any losses. Studies show that mineral deficiencies are extremely rare among people who consume well-balanced high-fiber diets. In addition to all the nutrients and health benefits, foods rich in fiber add more flavor and texture to your diet.
The National Cancer Institute recommends we eat 20 to 35 grams of fiber a day, but the average American only consumes about 11 grams daily. Increase your fiber consumption gradually to avoid intestinal gas, bloating and cramps caused by fermentation of fiber. Eat small portions of high-fiber foods at each meal in the beginning. Once the bacteria in your system adjust to the fiber increase, there is less chance of experiencing undesirable side effects. It's also important to drink plenty of water—six to eight glasses a day—when adding fiber to your diet. Without sufficient water, fiber can promote constipation.
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