Soy foods remain a controversial topic in sports nutrition, as well as in general health considerations. If you were to believe many of the web sites that discuss soy, you would think that soy has little or no beneficial effects and if anything, can produce a number of negative effects on health. Some of the common critiques often leveled against soy are that it raises estrogen levels and lowers testosterone. If that were true, ingesting any type of soy product would be considered anathema to any rational bodybuilder or athlete. Another problem is an alleged interference with the production of thyroid hormones in the body. Since the thyroid gland hormones control resting metabolism, any interference with the synthesis of those hormones could have far-ranging effects, not the least of which is a greater tendency to gain body fat, or a decreased ability to lose body fat even while on a stringent diet. The research on soy has greatly increased in recent years and has examined many of the claims made about soy, both good and bad. We will take a look at this research in this article.
In bodybuilding, soy protein was the first popular protein supplement. Soy is unique among vegetable proteins in that it is a complete protein source. What that means is that soy contains all the nine essential amino acids required for optimal growth. Just reading that would make you think that soy protein is as good as some of the more popular animal-based proteins, such as whey. But this may or may not be the case. While soy does contain all essential amino acids, it tends to be lower in at least one of them, methionine. But this may not be as bad as it initially appears to be, since animal studies have consistently found that if you lower methionine intake in the animals, it extends their lifespan. Although there is as yet no evidence that this also happens in humans, one aspect of methionine metabolism definitely does limit lifespan in humans. A byproduct of methionine metabolism called homocysteine is associated with cardiovascular disease and degenerative brain disease. However, this toxic byproduct of methionine metabolism can easily be controlled by ingesting nutrients that will neutralize the toxic effects of homocysteine, such as vitamins B12, B6, and folic acid.
When I first got into bodybuilding 58 years ago, soy protein supplements were the most popular selling protein supplements. This was largely due to the efforts of Bob Hoffman, who published two bodybuilding magazines, Strength and Health and later in 1964, Muscular Development. In those magazines, Hoffman greatly pushed his in-house protein supplements, which were entirely derived from soy. The York Barbell Company, Hoffman's company, did produce another short-lived protein called "Protein from the Sea" that earned the dubious reputation as the worst tasting and mixing protein supplement in recorded history. But while his soy protein products were not exactly delicious, they were at . . .