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.

Low energy availability in exercising men is associated with reduced leptin and insulin but not with changes in other metabolic hormones

“…In field studies in male soldiers, 25%-50% reductions in IGF-1 and testosterone have been reported during strenuous field training involving energy deprivation (Alemany et al, 2008;Friedl et al, 2000;Kyrolainen et al, 2008;Nindl et al, 2007Nindl et al, , 1997. However, these field studies were not conducted under controlled conditions and involved severe energy deficits of 1000-4000 kcal · day −1 as opposed to quantifiable measures of energy availability (Alemany et al, 2008;Friedl et al, 2000;Kyrolainen et al, 2008;Nindl et al, 1997Nindl et al, , 2007. It is possible that low basal leptin concentrations, which were in agreement with the low body fat percentage (9.6 ± 1.5%), acted to prevent changes in testosterone, IGF-1 and T3.…”

Longitudinal trends in use of dietary supplements by U.S. Army personnel differ from those of civilians

“…weight loss, may reflect the desire of soldiers to retain lean body mass while under energy restriction. Soldiers perform a wide range of physically demanding occupational tasks, which can decrease sex steroids (Alemany et al 2008) and deplete micronutrient stores when energy intake is restricted (Lukaski 2004). Thus, patterns of DS use may reflect the need to regulate body weight in an occupational field that is physically demanding and requires sustainment of energy levels to perform required job duties.…”

Suplementação com carboidratos durante treinamento intensivo aumenta as concentrações de lipídios intramiocelulares e reduz os marcadores de lesão tecidual em corredores competitivos: interação hormonal e metabólica

“…Thus, the nutritional intervention used for both groups over the 8 days of training was eVective in preserving the metabolic and hormonal proWles indicating attenuation of metabolic stress. These Wndings corroborate the studies of Alemany et al (2008), and indicating that in comparison with athletes eating a diet restricted in energy and protein, the hormones testosterone, IGF1 and IGFBP3 are maintained at normal physiological concentrations when energy intake is adequate. In this study runners from both groups showed similar energy intake, and as suggested by this condition could help explain why IGFBP3 levels were maintained.…”