Effects of dietary protein content on IGF-I, testosterone, and body composition during 8 days of severe energy deficit and arduous physical activity

J Appl Physiol (1985). 2008 Jul;105(1):58-64. doi: 10.1152/japplphysiol.00005.2008. Epub 2008 May 1.


Energy restriction coupled 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. The aim of this study was to 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 higher dietary protein content would attenuate the decline of anabolic hormones and, thus, prevent losses of fat-free mass. Thirty-four men [24 (SD 0.3) yr, 180.1 (SD 1.1) cm, and 83.0 (SD 1.4) kg] participated in an 8-day military exercise characterized by high energy expenditure (16.5 MJ/day), low energy intake (6.5 MJ/day), and sleep deprivation (4 h/24 h) and were randomly divided into two dietary groups: 0.9 and 0.5 g/kg dietary protein intake. IGF-I system analytes, androgens, and body composition were assessed before and on days 4 and 8 of the intervention. Total, free, and nonternary IGF-I and testosterone declined 50%, 64%, 55%, and 45%, respectively, with similar reductions in both groups. There was, however, a diet x time interaction on day 8 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). Dietary protein content of 0.5 and 0.9 g/kg minimally attenuated the decline of IGF-I, the androgenic system, and fat-free mass during 8 days of negative energy balance associated with high energy expenditure and low energy intake.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Androgens / metabolism
  • Body Composition / drug effects*
  • Dietary Proteins / pharmacology*
  • Energy Intake / physiology*
  • Energy Metabolism / physiology
  • Food Deprivation / physiology
  • Humans
  • Insulin-Like Growth Factor Binding Proteins / blood
  • Insulin-Like Growth Factor I / metabolism*
  • Male
  • Military Personnel
  • Motor Activity / physiology*
  • Testosterone / metabolism*


  • Androgens
  • Dietary Proteins
  • Insulin-Like Growth Factor Binding Proteins
  • Testosterone
  • Insulin-Like Growth Factor I