Soy protein supplementation increases serum insulin-like growth factor-I in young and old men but does not affect markers of bone metabolism
Khalil DA, Lucas EA, Juma S, et al. J Nutr 2002;132:2605-2608.
Recent studies suggest that soy protein (SP) protects bone in women; however, its effects on bone metabolism in men have not been investigated. Healthy men (59.2 +/- 17.6 y) were assigned to consume 40 g of either SP or milk-based protein (MP) daily for 3 mo in a double-blind, randomized, controlled, parallel design. Serum insulin-like growth factor-I (IGF-I), which is associated with higher rates of bone formation, was greater (P /=65 y and those <65 y of age. The response to protein supplementation was consistent in the two age groups. The effects of SP on serum IG-I levels suggest that SP may positively influence bone in men. Longer-duration studies examining the effects of SP or its isoflavones on bone turnover and bone mineral density and content in men are warranted.
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