Review of clinical studies on cholesterol-lowering response to soy protein.

Experiments on animals have shown that soybean protein has hypocholesterolemic and antiatherogenic properties. In human beings, substitution of soy protein for dietary animal protein or addition of soy protein to the diet lowers total and low-density-lipoprotein cholesterol levels in individuals with hypercholesterolemia. Reductions of 20% or more have been obtained with diets high in protein (about 20% of total energy) and relatively low in fat. Triglycerides are also decreased, particularly in subjects with hypertriglyceridemia, but soy-protein diets appear to have little effect on high-density-lipoprotein cholesterol levels. Responses are similar in men and women, but may be greater in younger than in older subjects. The hypocholesterolemic effect is thought to be mainly attributable to the protein itself rather than to nonprotein components of soy-protein preparations. The mechanism of action is not known, and it may not be possible to explain the observed effects in human beings and in experimental animal models by the same mechanism. Although the hypocholesterolemic response to dietary soy protein has been observed by a number of European research groups, substitution of soy protein for animal protein in North American diets has generally had little effect, for reasons that are still not clear.