Anyone wishing to gain lean muscle mass must appreciate the significance of protein. Not only is protein crucial for hypertrophy, but it is also necessary for growth and repair when training for strength and power. The debate continues in terms of the ideal type of protein, but multiple scientific findings and real-world applications point to the value of ingesting whey protein before and after training. A relatively new area of investigation — that so far has seen only limited prior research — is the topic of protein supplementation and testosterone production.
A recent study in the Journal of the American College of Nutrition led by William Kraemer, Ph.D., of the University of Connecticut, examined the effects of soy protein versus whey protein supplementation on the responses of testosterone, sex hormone-binding globulin (SHBG) and cortisol in men. Many trainers and coaches have expressed concerns regarding soy’s pro-estrogen and testosterone-limiting effects. This study provided some overdue clarity on this topic.
Ten resistance-trained men in their early 20s were randomized in crossover-balanced placebo design that consisted of three treatment groups: whey protein isolate, soy protein isolate and a placebo control group that received maltodextrin. No other supplements were allowed, and vegetarians, vegans or subjects who consumed high-protein diets were excluded from the study.
For two weeks, participants ingested 20 grams of their assigned supplement at the same time each morning. The participants performed six sets of heavy squats at 10 reps, each using 80 percent of their 1RM. The subjects’ serum hormone concentrations were tested postworkout. After a two-week washout period, the participants repeated the experiment using the alternative protein or carbohydrate source.
The main findings of this study showed that postworkout testosterone levels were significantly decreased when subjects used soy protein compared to whey protein. Further, consuming whey protein promoted the same level of testosterone as consuming the carbohydrate. This has implications that soy protein has a direct negative effect on testosterone levels. In addition, whey protein supplementation produced a significant postworkout decrease in cortisol levels relative to soy protein or carb supplementation.
Overall, this study shows that soy protein supplementation reduces testosterone, possibly blunting the anabolic response following a workout. The results suggest that those interested in adding muscle should consume whey protein rather than soy.
In another investigation, researchers in Finland examined the impact of protein ingestion on circulating testosterone and muscle androgen receptors, as well as on insulin-like growth factor-1 responses to resistance exercise in older men. The subjects were fed 15 grams of whey protein isolate or a placebo before and after a workout (five sets of 10RMs). Muscle biopsies were taken before the workout, and at one hour and 48 hours postworkout to examine the expression of androgen receptors.
Although the androgen receptor mRNA responses were variable, they tended to increase more during the whey protein isolate group than in the placebo group. The average increase one hour post-exercise was about 25 percent, and this was maintained up to 48 hours after the workout. In contrast, there was little change in average androgen receptor expression during the placebo trial. (One takeaway point is that even older men are able to increase muscle androgen receptor mRNA expression in response to resistance training.)
It’s important to note that the researchers speculated that the greater expression of androgen receptors in skeletal muscle may allow for greater uptake of testosterone from the blood. This might be one way in which whey protein enhances anabolism in response to strength-training bouts.
Due to the limited prior research exploring the topic of protein supplementation and testosterone production, more studies are needed. However, based upon current findings, whey protein certainly exhibits a positive and favorable impact on hormonal response.