Dietary Fiber and Lipid Metabolism

The hypothesis that dietary fiber alters cholesterol levels by adsorbing bile acids, which would increase their excretion and alter cholesterol absorption, appears to be too simplistic based on the accumulated data. Some sources of dietary fiber (e.g., oat bran) reduce serum and/or liver cholesterol levels and simultaneously increase steroid excretion. However, these changes do not seem to be of a magnitude sufficient to account for the change in serum cholesterol. In addition, other sources which cause more substantial increases in steroid excretion cause no change in cholesterol accumulation (e.g., corn bran or cellulose) and, in humans, a reduction in serum cholesterol by beans is accompanied by a reduction in steroid excretion. A change in bile acid pool sizes in response to oat bran and the effects this may have on sterol balance may be an additional mechanism for the observed effects. Other situations (i.e., beans) do not fit either of the above mechanisms and will require further investigation.