Studies have suggested that the phytoestrogens contained in soy protein lead to both unwanted decreases in testosterone, and increases in the female sex hormone estrogen.
For example, the isoflavones (a phytoestrogen) found in soy are thought to upset hormone balance, and result in the aforementioned unwanted testosterone and estrogen changes in addition to thyroid problems.
Some nutritional counselors have begun to suspect that soy may be to blame for the low energy, digestive disturbances, hypothyroidism, infertility, and other ailments they see in clients.
However, on the other side of the coin, many scientists believe soy to be relatively innocuous, and in fact beneficial for a whole range of physical ailments.
IS SOY BENEFICIAL?
Soy protein, extracted from the annual leguminous soybean plant that has been in the food chain for over 5,000 years, is the only plant-based protein considered to be a high-quality protein, containing all of the essential amino acids in the ratios needed to support growth and development..
The soybean was introduced to the US in the 1880s, and before then was, and still is, a staple of the Asian diet.
Soy is comprised of 30% carbohydrate (15% of this is fibre), 38% protein, 18% oil (85% of this unsaturated), and 14% moisture11. Soy contains all nine essential amino-acids, in the perfect ratio for health and well-being.
Soy's other nutritional functions include providing a respectable amount of potassium, zinc, iron, vitamin-E, phosphorous as well as the full B-complex.
Used together in an exercise regimen, soy and whey proteins complement each other well. Whey protein, as mentioned, is high in branched chain amino acids, used as an important energy source by the body during exercise, while soy protein has high amounts of the amino acids arginine and glutamine.
Arginine is well known as a stimulant of anabolic hormones that stimulate muscle formation, while glutamine is considered essential during metabolic stress.