Fiber & Weight Loss

Below is an excerpt from Part Two of

The 2004 Multi-Diet

by Anderson A. Anonymous, M.D., Ph.D.

More On… Fiber

Keep it moving, folks, keep it moving.

Background

The RDI of fiber is 20–30 grams/day. Over the years many researchers have suspected that dietary fiber can somehow help you lose weight. The threshold theory suggests that it does—though not exactly for the reasons most often discussed.

There have been a number of scientific hypotheses about how fiber might help people lose weight.

1. Perhaps it may help directly reduce food intake in some way.
2. Perhaps in some way it may cause less of the energy in food to be absorbed.
3. Perhaps it somehow stimulates “secondary metabolic activities” that affect the use of absorbed energy in some beneficial way.

In 1976 dietary fiber was defined as “plant polysaccharides and lignin resistant to digestion by the small intestinal enzymes of man”.

This means that what is called “fiber” is really a very “mixed bag” of different substances. “Different” may also mean different in physical properties as well as chemical ones. For example, fiber that typically has tiny particle sizes may have completely different effects in the intestine than fiber which stays in relatively large chunks—even if the two types are chemically identical.

One researcher has pointed out that the presence of fiber usually has secondary effects on other food components. For example, if you eat a diet high in fiber this often means that it is also higher in carbohydrates and lower in fat and sodium than low-fiber diets.

It is therefore also likely to be lower in “energy density” (carbohydrate has fewer Calories per gram than fat)—thus it will have a different effect than a low-fiber diet. However, in this case, the different effect is not a direct effect of the fiber on the body, but an effect of the fiber on other nutrients in the diet. (In this case, it displaces them.)

Experiments attempting to find out whether eating fiber reduces hunger and food intake have been inconclusive. Those that show there is an effect are contradicted by others that show no effect. Researchers believe that the weight of evidence demonstrates that fiber sometimes really does reduce hunger and eating behavior, but not always. The reasons for this are still speculative.

Experiments have been slightly more successful in finding out the effect of fiber on energy absorption. In general they have shown that fiber causes a small but measurable loss of energy because of non-digestion. In other words, on high fiber diets a small amount of the energy in food “passes through” without getting absorbed.

Unfortunately, it’s a very small amount—probably in the range of 30-180 Calories per day. Of course, as I’ve pointed out, over a period of time this amount of energy can put on considerable weight. Unfortunately, by this means alone, it would require just as long to take it off again.

Therefore, realistically, this effect of fiber is probably by itself too small to build a successful weight loss plan on. The beneficial effect is too easily overridden by even one “accidental” high-calorie meal. However, we dieters need every advantage we can get, and we are glad to see evidence that fiber can be even a small part of real weight loss.