Henning, P. C., Margolis, L. M., McClung, J. P., Young, A. J., & Pasiakos, S. M. (2014). High protein diets do not attenuate decrements in testosterone and IGF-I during an energy deficit. Medicine & Science in Sports & Exercise, 46(5), Supplement abstract number 386.

“Energy deficit diminishes fat-free mass with concomitant reductions in anabolic-hormone secretion. Although consuming high-protein diets preserves fat-free mass during energy deficit, the effects of dietary protein on circulating anabolic hormones and their potential relationships with fat-free mass in response to short-term energy deficit are not well described.”

This study determined the anabolic hormonal response to habitual consumption of high protein diets during short-term energy deficit, and evaluated whether modulations in testosterone and IGF-I components are associated with the documented preservation of fat-free mass subsequent to consuming high-protein diets. Adults (N = 33) were assigned diets providing protein at 0.8 recommended dietary allowance, 1.6, and 2.4 g/kg/day for 31 days. Testosterone, sex-hormone binding globulin, and insulin-like growth factor I (IGF-I) system components were assessed after a 10-day period of weight-maintenance followed by a 21-day period of energy deficit (40%). Associations between the change in fat-free mass and anabolic hormone levels were determined.

Compared to weight maintenance and regardless of dietary protein intake, there was a decrease in total testosterone, free testosterone, total IGF-I, and acid-labile subunit, whereas sex-hormone binding globulin, IGF binding proteins, IGFBP-2 and IGFBP-3 increased during energy deficit. There were no energy-by-protein interactions on any measured hormones or IGF-I system components. Changes in fat-free mass in response to energy deficit were negatively associated with ALS (r = -0.62) in the 2.4 g/kg/day condition. No other relationships were observed.

Implication. A high-protein diet does not impact the androgenic and IGF-I system responses to short-term energy deficit. The protective effects of high protein diets on fat-free mass during energy deficit are likely not influenced by anabolic hormone concentrations.

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