Nutrition experts used to debate the effectiveness of soy protein for promoting muscle growth. Critics of soy claimed that because the plant protein contains phytoestrogens—natural chemicals with a structure similar to estrogen—soy could lower testosterone levels and boost estrogen. But several research studies have confirmed that soy protein doesn’t alter levels of testosterone or estrogen. Even a recent study claiming that soy lowered T levels was debunked.

The Benefits of Soy

Since soy protein, particularly soy protein isolate, is fairly fast-digesting and rich in arginine, the amino acid that’s regularly converted to nitric oxide (NO) in the body, we now recommend adding soy to your pre-workout whey protein shake.

Research from Virginia Polytechnic Institute and State University (Blacksburg) confirms that consuming soy before training is a good idea not only because of its high arginine content but also because it directly stimulates NO production. The researchers reported in a 2008 issue of the Journal of Nutrition that genistein—one of the major phytochemicals in soy—increased the amount of nitric oxide synthase, an enzyme that catalyzes the arginine-NO conversion. Therefore, because soy protein is rich in both arginine and genistein, taking it before workouts increases NO levels and blood flow to the muscles.

Mix 10 grams of soy protein isolate with 10 grams of whey protein isolate within 30 minutes of workouts. Whey provides peptides (small proteins) that enhance blood flow by a mechanism not involving NO, so using both whey and soy will maximize blood flow to your muscles. This makes more nutrients, oxygen and anabolic hormones available to your exercising muscles and produces greater energy, a bigger pump, and enhanced recovery and growth postworkout.

Protein Prelude

Try this mix of proteins within 30 minutes before workouts for greater energy, muscle pump, recovery and growth.

Protein Amount
Whey protein isolate 10 g
Soy protein isolate 10 g