Energy restriction with high energy expenditure from arduous work is associated with an altered insulin-like growth factor-I (IGF-I) system and androgens that are coincident with losses of fat free mass. Purpose: Determine the effects of two levels of dietary protein content and its effects on IGF-I, androgens, and losses of fat free mass accompanying energy deficit. We hypothesized that increased dietary protein content would attenuate the decline in anabolic hormones preventing losses in fat free mass. Methods: Thirty-four men [24 (0.3) y, 180.1 (1.1) cm, 83.0 (1.4) kg] participated in an eight-day military exercise characterized by high energy expenditure (16.5 MJ/d), low energy intake (6.5 MJ/d), and sleep deprivation (4 h/24 h) were divided into two groups of 0.9 g/kg or 0.5 g/kg dietary protein. IGF-I system analytes, androgens and body composition were assessed throughout the intervention. Results: Total, free and non-ternary IGF-I as well as testosterone declined 50%, 64% 55% and 45%, respectively, with similar reductions both groups, except that there was a diet x time interaction on day eight for total IGF-I and sex-hormone binding globulin. Decreases in body mass (3.2 kg), fat-free mass (1.2 kg), fat mass (2.0 kg) and percent body fat (1.5 %) were similar in both groups (p = 0.01). Conclusion Dietary protein content of 0.5 or 0.9 g/kg had minimal effects in attenuating the decline in the IGF-I and androgenic systems and fat-free mass during eight days of negative energy balance associated with high energy expenditure and low energy intake.