The case for limiting soy: You simply don't use it

We’ve heard for years that soy protein isn’t ideal for male bodybuilders – not only that it’s often “incomplete” but also that it may have potent hormonal effects similar to estrogen, and that soy consumption may lead to lower testosterone levels and estrogenic effects. While the scientific evidence has shown that ingested soy protein does in fact not produce these effects, the debate still rages in some circles, with some experts recommending that male bodybuilders avoid ingesting soy protein altogether.

A new study on soy protein derived from wheat gives us another reason to limit our soy intake: Your body simply might not use it.

The study examined the retention of consumed wheat-derived soy protein, both before ingesting other forms of protein and afterward, in order to measure the effects of a high-protein diet on soy protein retention and utilization. The researchers found that when protein from other sources was eaten prior to ingesting soy protein, soy protein utilization and nitrogen retention was reduced dramatically.

So here’s your FUSION FACTOID: Although you shouldn’t avoid soy protein on the basis of possible hormonal issues, you should limit its consumption if you’re already eating a lot of protein from other sources. In the presence of these other types of protein, your body shies away from using soy protein in favor of the other kinds, so it becomes of limited benefit for muscle building.

- The Educated Bodybuilder

Source: Am J Clin Nutr. 2008;87:666–78.