Soy protein intake by active young adult men raises plasma antioxidant capacity without altering plasma testosterone

Soy protein contains antioxidant factors, such as isoflavones, which may help prevent heart disease and cancer. Nonetheless, many active men avoid soy protein because of reports that isoflavones lower testosterone levels. However, soy isoflavone effects on testosterone readings in active young adult males have not been reported. This study found that in such men, a 4-week intake of high-isoflavone soy protein (41.5 g/70 kg body weight per day) had no effect on plasma testosterone values. The soy protein intake did elevate plasma total antioxidant status values (a measure of free radical scavenging). By comparison, intake of whey protein or a placebo (cake mix) had no effect on plasma total antioxidant status readings. Thus, soy protein was found to produce an antioxidant effect in active young adult men without lowering testosterone concentrations.