title: Effects of dietary protein content on IGF-I, testosterone, and body composition during 8 days of severe energy deficit and arduous physical activity.
abstract: 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.
authors.affiliation: Military Performance Division, US Army Research Institute of Environmental Medicine, Natick, MA 01760, USA.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Alemany
authors.forename: Bradley C
authors.initials: BC
authors.lastname: Nindl
authors.forename: Mark D
authors.initials: MD
authors.lastname: Kellogg
authors.forename: William J
authors.initials: WJ
authors.lastname: Tharion
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Young
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Montain
mesh_terms: D000328:Adult; D000728:Androgens / Q000378:metabolism; D001823:Body Composition / Q000187:drug effects*; D004044:Dietary Proteins / Q000494:pharmacology*; D002149:Energy Intake / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology; D005508:Food Deprivation / Q000502:physiology; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008889:Military Personnel; D009043:Motor Activity / Q000502:physiology*; D013739:Testosterone / Q000378:metabolism*
chemical_list: D000728:Androgens; D004044:Dietary Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D013739:Testosterone; D007334:Insulin-Like Growth Factor I