Fiber Facts

Is the best way to get more fiber to add bran to our highly refined diets?

Kenneth I. Burke, Ph.D., R.D., is a food chemist and an associate professor of nutrition in the School of Health, Loma Linda University, Loma Linda, California.

NUTRITIONISTS TODAY advocate a high-fiber diet. This isn't really new. In the 1920's it was also popular for nutritional experts to recommend a highroughage diet. Is this just a fashion or a fad that is repeating itself?

First of all, we need to consider what is meant by dietary fiber. This term is used to indicate those plant constituents that resist digestion by the human gastro-intestinal tract, including various carbohydrate compounds such as cellulose, hemicellulose, pectin, and gum, as well as noncarbohydrates like lignin, the strengthening substance in wood plant cells. Fiber is often called "unavailable carbohydrate," but that is really not quite true, since it is not strictly unavailable nor is it entirely carbohydrate. Small portions disappear during digestion, probably because of the action of intestinal bacteria.

Unfortunately, it is extremely difficult to analyze for dietary fiber in the lab oratory because the analysis must approximate the digestive processes of man. However, there is an inexpensive laboratory determination that is easy to perform in the laboratory and gives the same answer every time—that of crude fiber. But it does not approximate human digestion either. It involves an arbitrary technique in which the product to be analyzed is dried, ground, boiled in dilute sulphuric acid solution for a given length of time, filtered, washed, and boiled again in dilute alkali (sodium hydroxide) for a specified time, and then dried, and burned to an ash. The difference between the weight of the ash and the dried product is considered crude fiber.

Crude fiber contains mainly cellulose and lignin. Hemicellulose, pectin, gums, and other products have been dissolved in the treatment with the acid and alkali. Keep in mind that crude fiber is not the same as real or dietary fiber. The pro portion of crude fiber to dietary fiber varies with each food.

Fiber should be added to the list of essential nutrients. The question is, then, is there a specific deficiency dis ease caused by lack of fiber in the diet? Unfortunately, there is no incontrovertible evidence that such a deficiency state exists, unless we call constipation such a state. But how about diverticulosis, hemorrhoids, cancer of the colon, and varicose veins? Aren't these dis eases also caused by lack of fiber in the diet? Burkitt and others, beginning around 1969, began to discover in specific populations an apparent relation ship of dietary fiber to incidence of intestinal disease. Burkitt's report on information from more than 200 hospitals in twenty countries was astounding —no population group that ate a highfiber diet had a high incidence of these bowel diseases. He further found that any population group that changed from a high-fiber to a low-fiber diet had a progressive increase in these diseases with in one generation. These findings, Burkitt intimated, were suggestive rather than conclusive, and indicated that the role of dietary fiber in disease certainly deserves more attention.

Does lack of fiber then cause diverticulosis, hemorrhoids, and other intestinal problems? The theory of the physiological interaction sounds plausible, but there have not been enough scientifically planned studies of human beings to establish it at this time.

Can high-fiber diets relieve diverticulosis and hemorrhoids? Probably so, but it is very difficult to separate out the psychological effects from the physio logical effects, since the large bowel is very sensitive to thought patterns. It would also be very difficult to design an experiment in which the patients did not know whether they were getting a highfiber or low-fiber diet, since a high-fiber diet naturally would increase the bulk of the stool.

The next question is: Can a high-fiber diet reverse the conditions of diverticulosis or cure diverticulosis? There is no evidence at this time that it can, but certainly a much larger, wetter stool can usually keep the symptoms to a mini mum.

Can colon cancer (the second most frequent cause of cancer deaths in the U.S.) be reduced with the aid of a high-fiber diet? No one knows for sure, but evidence from population studies suggests it can. Burkitt suggested that the possible relationship of low dietary fiber to in creased incidence of colon cancer results from the increased time it takes feces, on a low-fiber diet, to be eliminated, thus allowing more time for diet-nurtured bacteria to form cancer-forming chemicals from bile salts.

Some experiments in both animals and humans seem to show that dietary fiber may lower blood cholesterol by binding bile salts and forcing the body to produce more, thus lowering the body's cholesterol supply. Obesity and diabetes mellitus may also be linked to low-fiber diets, because these diets have greater calorie concentration, and people get more calories with less bulk. Foods that contain fiber also require more chewing, which slows eating and allows sufficient time for the satiety (fullness) center of the brain to signal that one has had enough to eat. Also, fiber reduces the efficiency of food absorption by the small intestine.

It has been stated that the amount of dietary fiber in the American diet has been greatly reduced during the past fifty years, but this claim is difficult to substantiate. There has been a decrease in the use of whole grain, but there has been a big increase in the use of fresh fruits and vegetables, which also contain fiber. The amount of water held by the different fiber constitutents in fruits and vegetables, as compared with cereals, varies, of course, with the cereal. It is generally thought that bran is able to hold and retain much water, therefore acting as a more efficient bulking agent than the fiber components of fresh fruits and vegetables.

There may be adverse effects of consuming large quantities of fiber. First of all, it may decrease the absorption of some minerals—for instance, calcium, magnesium, zinc, and phosphorus. In large amounts, it may temporarily in crease abdominal gas. It might be harmful to patients with ulcerative colitis, regional ileitus, or diverticulitis, until the inflammation clears. Large amounts of bran and other bulk-producing agents should not be eaten dry because of the possibility of causing an obstruction in the esophagus.

Is the best way to get more fiber in our diet to add bran to our highly refined diets? That may be somewhat helpful, but the ideal involves formulating a different way of eating, emphasizing an abundance of fruits and vegetables, grains, which are all there without loss of germ and/or bran, and well-cooked legumes. A simple but deliciously prepared nutritious diet provides plenty of fiber and avoids the pitfalls that can be found on either side of the fiber question.


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Kenneth I. Burke, Ph.D., R.D., is a food chemist and an associate professor of nutrition in the School of Health, Loma Linda University, Loma Linda, California.

November 1976

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