ISCB Honors Michael S. Waterman and Mathieu Blanchette

Background: Evidence suggests an inverse relationship between soy protein intake and serum concentrations of male sex hormones. Anecdotal evidence indicates that these alterations in serum sex hormones may attenuate changes in lean body mass following resistance training. However, little empirical data exists regarding the effects of soy and milk-based proteins on circulating androgens and exercise induced body composition changes. Methods: For 12 weeks 20 subjects were supplemented with 50 g per day of one of four different protein sources (Soy concentrate; Soy isolate; Soy isolate and whey blend, and Whey blend only) in combination with a resistance-training program. Body composition, testosterone, estradiol and sex hormone binding globulin (SHBG) were measured at baseline and week 12. Results: Protein supplementation resulted in a significant increase in lean body mass independent of protein source (0.5 ± 1.1 and 0.9 ± 1.4 kg, p = 0.006, p = 0.007). No significant differences were observed between groups for total and free testosterone, SHBG, percentage body fat, BMI or body weight. The Testosterone/Estradiol ratio increased across all groups (+13.4, p = 0.005) and estradiol decreased (p = 0.002). Within group analysis showed significant increases in the Testosterone/Estradiol ratio in soy isolate + whey blend group (+16.3, p = 0.030). Estradiol was significantly lower in the whey blend group (-9.1 ± 8.7 pg/ml, p = 0.033). Conclusion: This investigation shows that 12 week supplementation with soy protein does not decrease serum testosterone or inhibit lean body mass changes in subjects engaged in a resistance exercise program. Background The maintenance of skeletal muscle mass can be defined as the net result of protein synthesis and degradation. In most healthy persons the consumption of regular meals without training results in a relatively stable balance of muscle tissue over time. Generally it is acknowledged that a combination of training and adequate nutrition promotes the accretion of lean body tissue; the presence of a Published: 23 July 2007 Journal of the International Society of Sports Nutrition 2007, 4:4 doi:10.1186/1550-2783-44 Received: 14 June 2007 Accepted: 23 July 2007 This article is available from: http://www.jissn.com/content/4/1/4 © 2007 Kalman et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.