Food fads may come and go, but the importance of a well-balanced diet never goes out of style. One of the most important components of a healthful diet is fiber, and while it may not be the most exciting part of the diet, the consumption of foods high in dietary fiber is essential to maintain good health and prevent many diseases. This recommendation is as strong today as when first proposed more than 20 years ago. Scientific studies continue to show support for this statement and provide new evidence to indicate the importance of having optimal amounts of dietary fiber in the diet.
Dietary fiber is only found in plants. Dennis T. Gordon, Ph.D., a researcher of nutrition and dietary fiber at North Dakota State University, defines fiber as "Food carbohydrates not digested nor absorbed and which contribute to positive physiological functions in the body." Dietary fiber consists of two types—soluble and insoluble. This differentiation refers to whether the fiber dissolves in hot water. It also helps explain how these two types of dietary fiber function in the intestine.
Old Favorites: Soluble and Insoluble Fiber
Soluble dietary fiber is found in all fruits and a few cereals (oats and barley), and as gums added to cereals and other foods. It is the softer, stickier and thicker fiber. More specific soluble fibers are pectins (in all fruits) and ß-glucan (in oats and barley). Pectins help fruits to hold water which gives them the textures we expect and enjoy. Another soluble fiber is psyllium. It comes from the dried husk of the psyllium seed, primarily harvested in India, and is an effective laxative when consumed in high amounts. It is an excellent source of fiber now found in hot and cold cereals and other foods.
Soluble fiber acts as a natural thickening agent in food. The ß-glucan in oats is a classic example of a soluble fiber imparting a gummy and sticky texture-think of oatmeal. This property observed in foods containing ß-glucan and other soluble fiber also occurs in our intestines. Soluble dietary fiber entraps fatty substances in the intestines preventing their absorption into the body, thus explaining how soluble dietary fiber may effectively lower blood cholesterol levels when consumed in adequate amounts.
The largest amount of dietary fiber in our diets is insoluble. It gives fruits, vegetables and cereals their physical appearance (think of wheat bran) and texture or mouth feel. Insoluble fiber is primarily found in chewy foods like whole wheat products, wheat and corn bran, the skin of fruits, and certain vegetables (like cauliflower). Insoluble fiber helps bind water in the intestine and expands the volume of the intestinal contents, resulting in more frequent and softer stools.
Dietary Partners
The combined actions of soluble and insoluble dietary fiber are important in helping to maintain a healthy population of bacteria in our large intestines. The dietary fiber in the large intestine serves as a source of energy for these bacteria and as physical sites for them to attach. The fermentation of dietary fiber in the large intestine helps promote the growth of more lactic acid-producing bacteria. A predominance of lactic acid-producing bacteria in our intestines helps prevent the accumulation of toxic and pathogenic (disease-causing) bacteria.
Disease Fighters
Too few Americans consume adequate amounts of fiber. Yet, not only is it easy to take steps to reach your dietary fiber intake goal, but it is also vital to good health. Dr. Gordon warned, "There are many diseases or disorders frequently related to inadequate consumption of dietary fiber. These diseases are cancer of the colon, high blood cholesterol, hypercholesterolemia/atherosclerosis, diabetes, diverticulosis, constipation, hypertension, obesity, gallstone formation and growth of pathogen organisms in the large intestine."
Under the Nutrition Labeling and Education Act of 1990, the Food and Drug Administration (FDA) is authorized to ensure the accuracy of health claims on food labels. The FDA has authorized health claims involving dietary fiber and two major diseases: coronary heart disease and some forms of cancer.
Coronary heart disease is the cause of death for thousands of Americans each year. The National Heart, Lung and Blood Institute found a direct relationship between blood cholesterol concentrations and premature coronary heart disease. Dietary fiber, particularly soluble fiber, appears to lower blood cholesterol concentrations and may help to reduce the risk of premature coronary heart disease.
Colorectal cancer is one of the most common forms of cancer. Although the evidence may not be complete, much research has shown that a low-fat, high-fiber diet may reduce the risk of this type of cancer. John D. Potter, M.D., Ph.D., Fred Hutchinson Cancer Research Center, noted that, "Since 1970, a large number of case-control studies have explored the role of dietary fiber in colorectal cancer, with relatively consistent results suggesting a reduced risk with higher consumption."
However, a study published in the January 21, 1999 issue of The New England Journal of Medicine reported that a high-fiber diet did not appear to affect the number of women in the test group who developed colon cancer. Dr. Potter suggested that a number of technical issues concerning this study need to be resolved, including the translation of dietary data collected in the test group's questionnaires, biological questions about fiber itself, and questions intrinsic to epidemiologic studies.
More research will undoubtedly be performed to determine what effect dietary fiber has on colon cancer. Nevertheless, the overall health benefits of dietary fiber are not controversial, and dietary fiber remains an important part of the diet. Drs. Gordon and Potter both agree that while one study alone will not prove a positive effect of dietary fiber on any human disease, no one study deserves to be the final word in dismissing the importance of dietary fiber for any disease.
Another disease that can be partially controlled by consuming soluble dietary fiber is non-insulin dependent diabetes. Soluble fiber, by delaying the absorption of glucose, appears to help maintain lower serum insulin concentration.
There is no doubt that dietary fiber is beneficial to your health, and more research will illuminate the areas in which dietary fiber will help maintain a healthful lifestyle. Remember, feeling and being healthy is always in fashion. Getting the recommended amount of dietary fiber is one way to help achieve that goal.
How much fiber is enough?
Most health organizations agree that adults should consume between 20 and 35 grams of dietary fiber each day.
If, like many Americans, you have not been consuming enough fiber, it is probably best to gradually increase your intake. This should eliminate minor problems some people experience with a rapid increase in fiber intake, including stomach and intestinal discomfort and gas.
With a little planning, it is easy to reach your dietary fiber intake goal. The dietary fiber content of packaged foods is listed on the Nutrition Facts Panel. By taking a minute to read food labels, you can begin to make good dietary fiber choices. Adding a serving of red kidney beans (half cup) to your chili adds 6.5 grams of fiber. A wheat bran-rich cereal can provide as much as 15 grams of fiber per serving whereas other cereals (although nutritionally beneficial in other ways) may provide less than one gram of fiber per serving. If you do not enjoy high-fiber choices, mixing a high-fiber cereal with a low-fiber cereal is one way to get some of the benefits of both.
