Appendix A: What About the Widely Advocated Dietary Restrictions on Fat, Protein, and Salt, and the Current High-Fiber Fad? / Read It Online!

PAGE   1  2  3  4

What About Dietary Fiber?

Get Entire Chapter (195K) Tip: To save without viewing, right-click and choose Save Target As from pop-up menu

"Fiber" is a general term that has come to refer to the undigestible portion of many vegetables and fruits. Some vegetable fibers, such as guar and pectin, are soluble in water. Another type of fiber, which some of us call roughage, is not water-soluble. Both types appear to affect the movement of food through the gut (soluble fiber slows processing in the upper digestive tract, while insoluble fiber speeds digestion farther down). Certain insoluble fiber products, such as psyllium, have long been used as laxatives. Consumption of large amounts of dietary fiber is usually unpleasant, because both types can cause abdominal discomfort, diarrhea, and flatulence. Sources of insoluble fiber include most salad vegetables. Soluble fiber is found in many beans, such as garbanzos, and in certain fruits, such as apples.

I first learned of attempts at using fiber as an adjunct to the treatment of diabetes about twenty years ago. At that time, Dr. David Jenkins, in England, reported that guar gum, when added to bread, could reduce the maximum postprandial blood sugar rise from an entire meal by 36 percent in diabetic subjects. This was interesting for several reasons. First of all, the discovery occurred at a time when few new approaches to controlling blood sugar had appeared in the medical literature. Second, I missed the high-carbohydrate foods I had given up, and hoped I might possibly reinstate some. I managed to track down a supplier of powdered guar gum, and placed a considerable amount into a folded slice of bread. I knew how much a slice of bread would affect my blood sugar, and so as an experiment, I used the same amount of guar gum that Dr. Jenkins had used, and then ate the concoction on an empty stomach. The chore was difficult, because once moistened by my saliva, the guar gum stuck to my palate and was difficult to swallow. I did not find any change in the subsequent blood sugar increase. Despite the unpleasantness of choking down powdered guar gum (which is often used in commercial products such as ice cream as a thickener), I repeated this experiment on two more occasions, with the same result. Subsequently, some investigators have announced results similar to those of Dr. Jenkins, yet other researchers have found no effect on postprandial blood sugar. In any event, a reduction of postprandial blood sugar by only 36 percent really isn't adequate for our purpose, since we're shooting for the same blood sugars as nondiabetics. This means virtually no rise after eating.

Dr. Jenkins also discovered, however, that the chronic use of guar gum resulted in a reduction of serum cholesterol levels. This is probably related to the considerable recirculation of cholesterol through the gut. The liver secretes some cholesterol into bile, which is released into the upper intestine. This cholesterol is later absorbed lower in the intestines, and eventually reappears in the blood. Guar binds the cholesterol in the gut, so that rather than being absorbed, it appears in the stool.

In the light of these very interesting results, other researchers studied the effect of foods (usually beans) containing other soluble forms of fiber. When beans were substituted for faster-acting forms of carbohydrate, postprandial blood sugars in diabetics increased more slowly, and the peaks were even slightly reduced. Serum cholesterol levels were also reduced by about 15 percent. But subsequent studies, reported in 1990, have uncovered flaws in the original reports, casting serious doubt upon any direct effect of these foods upon serum lipids. In any event, postprandial blood sugars were rarely normalized by such diets.

Many popular articles and books have appeared advocating "high-fiber" diets for everyone—not just diabetics. Somehow, "fiber" came to mean all fiber, not just soluble fiber, even though the only viable studies had utilized such products as guar gum and beans.

In my experience, reduction of dietary carbohydrate is far more effective in preventing blood sugar increases after meals. The lower blood sugars, in turn, bring about improved lipid profiles.

A recent food to join the high-fiber trend is oat bran. This has gotten a lot of play in the popular press. Recently, a patient of mine started substituting oat bran muffins for protein in her diet. Before she started, her HgbA1C (see Chapter 2) was within the normal range and her ratio of total cholesterol to HDL was very low (meaning her cholesterol risk ratio was low). After three months on oat bran, her HgbA1C became elevated and her cholesterol-to-HDL ratio nearly doubled. I tried one of her tiny oat bran muffins after first injecting 3 units of fast-acting insulin (nearly as much as I use for an entire meal). After 3 hours, my blood sugar went up by about l00 mg/dl, to 190 mg/dl. This illustrates the adverse effect that most oat bran preparations can have upon blood sugar. The reason for this is that most such preparations contain flour. On the other hand, I find that certain bran products, such as the bran crackers listed in Chapter 10, raise blood sugar very little. This is because, unlike most packaged bran products, they contain mostly bran and little flour. They therefore have very little carbohydrate. You can perform similar experiments yourself—just use your blood glucose meter. Beware of commercial "high-fiber" products that promise cholesterol reduction. If they contain carbohydrate, they must at least be counted in your meal plan and will probably render little or no improvement in your lipid profile.

Fiber, like carbohydrate, is not essential for a healthy life. Just look at the Eskimos and other hunting populations that survive almost exclusively on protein and fat, and don't develop cardiac or circulatory diseases.*

What Diet Will Work for You?

PAGE   1  2  3  4