For vegans and vegetarians, soy protein powder offers an excellent alternative to whey as a protein source. Its complete protein includes all 9 essential amino acids and can aid with muscle development as well as offers a useful option for meal replacement on a weight loss diet.
Additionally, research suggests that soy protein can offer health benefits including helping prevent cardiovascular disease, and reducing the risk of some cancers as well as bad cholesterol levels.
It's not all good though. Soy protein is less effective in delivering amino acids to your body than whey. Soy protein also contains isoflavones, which include phytoestrogens that mimic the hormone estrogen in your body. It's been widely suggested that this could have effects on testosterone levels in men when consumed in large quantities. Soy is also fairly low in the amino acid Methionine which is important for muscle development. Though many products add additional Methionine to make up for this deficiency.
While there are negatives, soy is one of the most widely used products we consume. It is generally considered very safe and proper use of soy protein powder as directed should not result in any significant problems.
However, we would not recommend soy protein powder during pregnancy due to some of the unique properties of soy protein on the baby's development.