Soy is probably the only non-animal source of protein that is of high quality. For instance, one study examined twenty-seven untrained healthy subjects age 18 to 35 years who were randomly assigned (double blind) to supplement with whey protein, soy protein or a sugar placebo.
Results showed that protein supplementation during resistance training, independent of source, increased lean tissue mass and strength over isocaloric placebo and resistance training.(1) Thus, both soy and whey are better than sugar. Another study compared soy versus whey. Lean body mass gain was examined in males from a university weight training class given daily servings of micronutrient-fortified protein bars containing soy or whey protein (33 g protein/day, 9 weeks).
Training used workouts with fairly low repetition numbers per set. Again, both the soy and whey treatment groups showed a gain in lean body mass, but the training-only group did not. In conclusion, soy and whey protein bar products both promoted exercise training-induced lean body mass gain, but interestingly, soy consumption had the added benefit of preserving two aspects of antioxidant function.(2) And another recent study found that differences in weight loss and body composition changes between casein and soy treatments were not significant.(3).
It should be apparent that soy is a good source of protein. If you are a vegan, than it would be wise to use soy protein, particularly during the pre and/or post-exercise window.
