Soy Beverage Consumption by Young Men

ABSTRACT

Consumption of soy components, such as isoflavones, is thought to produce antioxidant effects, but this is largely unconfirmed by human studies. The present study found that 3 week consumption of a soy beverage (2 servings/day, 40 g protein and 44 mg of the isofla-vone genistein/day) increased plasma total antioxidant status values in each of 10 young adult males. In 10 other males, consuming a whey beverage (40 g protein/day) depressed plasma total antioxidant status values. Soy and whey consumption were also examined for effects on muscle tissue breakdown after a bout of strenuous aerobic exercise, a form of oxidant stress. The bout was performed before and after the 3 week soy or whey period. Compared to the first exercise bout, soy produced a lower rise in plasma creatine kinase activity, an indicator of muscle tissue breakdown (whey produced a higher rise). Soy also reduced the post-exercise rise in plasma myeloperoxidase, an indicator of inflammatory oxidant stress (whey had no effect). In addition, soy maintained, while whey decreased, the post-exercise rise in plasma uric acid (which can be inversely proportional to oxidant activity). These results provide evidence that soy can exert antioxidant effects in people, particularly for exercise-induced oxidant stress.

Key Words:

• Soy
• antioxidant status
• exercise
• muscle tissue breakdown