Effect of protein source and resistance training on body composition and sex hormones

Abstract

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.

Figure 1

Mean (± SD) lean body mass measured at baseline and following 12 weeks of protein supplementation and resistance exercise. At week 12, group analysis shows a significant enhancement in lean mass (0.9 kg, p = 0.007). A trend towards significance within groups was present only in the soy isolate group (p = 0.055).

Figure 2

Mean (± SD) of total testosterone at baseline and following 12 weeks of protein supplementation and resistance exercise. No significant changes between or within groups were evident at week 12.

Figure 3

Mean (± SD) of free testosterone at baseline and following 12 weeks of protein supplementation and resistance exercise. No significant changes between groups were evident at week 12.

Figure 4

Mean (± SD) of testosterone/estradiol ratio following 12 weeks of protein supplementation and resistance exercise. As significant increase in the testosterone/estradiol ratio between groups was noted (+13.4, p = 0.005). The testosterone/estradiol ratio within the SW group was higher at week 12 in comparison to baseline measurements (+16.3, p = 0.030). * Indicates significant difference (p < 0.05)

Figure 5

Mean (± SD) of SHBG at baseline and following 12 weeks of protein supplementation and resistance exercise. No significant changes between or across groups were evident at week 12.

Figure 6

Mean (± SD) of estradiol at baseline and following 12 weeks of protein supplementation and resistance exercise. Serum estradiol was significantly lower in all four groups following supplementation and training (p = 0.002). Within group analysis shows a significant decrease in the WB intervention was statistically significant (-9.1 pg/ml, p = 0.033). * Indicates significant difference (p < 0.05)