Whey promotes more favorable hormonal response than soy in men
by Jeff S. Volek, Ph.D., R.D.
In evaluating the best protein for promoting anabolism and recovery, most research has focused on measures of muscle protein synthesis and points to whey as being the best choice. But other protein sources may be effective too such as soy.
Another important aspect of the recovery process is related to promoting an optimal hormonal environment, especially as it pertains to the anabolic hormone testosterone and the catabolic hormone cortisol. Studies evaluating the effects of protein quantity and quality have produced mixed results, but there is some evidence that soy protein may increase estradiol or have other effects on steroid hormones.
Until recently, no studies directly examined the acute hormonal response to resistance exercise after consumption of soy and whey protein. Our laboratory group therefore examined how consuming equal amounts of whey and soy protein affected hormonal responses to an intense squat workout in resistance-trained men.
For 2 weeks subjects consumed 20 grams of either whey isolate, soy isolate or carbohydrate each morning. Then they performed 6 sets of 10 repetitions of squat exercise 20 minutes after consuming the drink. Testosterone levels during exercise increased similar amounts in the whey, soy and carbohydrate group. Then immediately after exercise, the soy group’s testosterone levels quickly dropped back to baseline in about 30 minutes while the whey and carbohydrate group experienced a gradual decline back to baseline in about 60 minutes. The normal cortisol “stress hormone” increase due to exercise was significantly reduced in the whey group after exercise, but not in the other two groups. High cortisol levels can slow fat burning.
In addition to the well documented superior burst in muscle protein synthesis associated with whey, it appears whey creates a more anabolic hormone profile compared to soy. Although these results point to a beneficial effect of whey, soy still contains all the essential amino acids and is a good choice for athletes who prefer a plant-based protein source.