Saturday, February 24, 2007

Protein Series Part II: The Science of Soy

Protein Series Part II

by Jose Antonio

Science proves the positives on Soy

Soy's reputation among a growing number of questioning minds isn't exactly sterling, particularly with fitness and physique athletes. In fact, asking a recreational bodybuilder to use soy protein would be like asking the French military to go battle without wine.

Nonetheless, when you take a cursory look at the recent data on soy, perception is in fact not reality. The true scientific translation is that soy is probably the only non-animal source of protein that is of high quality.

For instance, one study examined 27 healthy, untrained subjects, ages 18 to 35, 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-level weight training class. They were given daily servings of micronutrient-fortified protein bars containing soy or whey protein (33g protein/day, 9 weeks). Training included workouts with fairly low repetitions per set. And again, both the soy and whey treatment groups showed a gain in lean body mass, but the training-only group did not. In conclusion, both soy and whey protein products promoted exercise training-induced lean body mass gain. Interestingly, soy consumption had the added benefit of preserving two aspects of antioxidant function.(2) Another recent study found that differences in weight loss and body composition changes, between casein and soy treatments, were not significant.(3)

Does soy affect female hormone levels? Well, yes and no. The data can be a little confusing. For instance, we know that eating soy protein has been associated with altered risk of developing endocrine-regulated cancers. One study looked at the effect of soy relative to animal protein and soy-derived isoflavones on circulating estrogen and androgen concentrations in both postmenopausal women and older men. In postmenopausal women, concentrations of estrone were higher and its precursor DHEA (dehydroepiandrosterone), lower after consuming the soy compared with animal protein diets. Estrone is one of the three naturally occurring estrogens, the others being estradiol and estriol. There was no significant effect of soy-derived isoflavones on any of the hormones measured. This study shows that relatively large amounts of soy protein or soy-derived isoflavones had modest and limited sex-specific effects on circulating hormone levels.(4) However, another study in healthy postmenopausal women showed that dietary soy isoflavones do not have an effect on biological indicators of estrogenicity. This suggests that soy isoflavones have little relevance or biological estrogenic effect on vivo in postmenopausal women.(5)

A moderate amount of soy containing foods should not be a problem. But if you are someone who is sensitive to the effects of soy, either cut the dose or eliminate it completely from your diet! It should be apparent that soy is a good source of protein for most. If you are a vegan, than it would be wise to use soy protein, particularly during your pre-exercise and/or post-exercise window.


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