Utility of circulating IGF-I as a biomarker for assessing body composition changes in men during periods of high physical activity superimposed upon energy and sleep restriction

Abstract

Young AJ, Montain SJ. Utility of circulating IGF-I as a biomarker for assessing body composition changes in men during periods of high physical activity superimposed upon energy and sleep restriction. J Appl Physiol 103: 340-346, 2007. First published April 5, 2007 doi:10.1152/japplphysiol.01321.2006.-Insulin-like growth factor (IGF)-I is a biomarker that may have greater utility than other conventional nutritional biomarkers in assessing nutritional, health, and fitness status. We hypothesized that the IGF-I system would directionally track a short-term energy deficit and would be more related to changes in body composition than other nutritional biomarkers. Thirty-five healthy men (24 Ϯ 0.3 yr) underwent 8 days of exercise and energy imbalance. Total and free IGF-I, IGF binding proteins-1, -2, and -3, the acid labile subunit, transferrin, ferritin, retinol binding protein, prealbumin, testosterone, triiodothyronine, thyroxine, and leptin responses were measured. Dual-energy X-ray absorptiometry assessed changes in body mass and composition. Repeated-measures ANOVA, correlation analysis, and receiver operator characteristic curves were used for statistical analyses (P Յ 0.05). Body mass (Ϫ3.8%), fat-free mass (Ϫ2.2%), and fat mass (Ϫ12.9%) all decreased. Total and free IGF-I, IGF binding protein-3, and the acid labile subunit and prealbumin, but not transferrin, retinol-binding protein, and ferritin, directionally tracked the energy deficit and losses in body composition. The correlation (r ϭ 0.43) between changes in free IGF-I and body and fat-free mass was the only significant association observed. Receiver operator characteristic curve analysis revealed that a baseline value Ͻ 1.67 for the molar volume ratio of IGF-I to acid labile subunit had an area under the curve of 0.745 and was a significant discriminator for those subjects losing Ͼ5% body mass. The IGF-I system is an important adjunct in the overall assessment of adaptation to stress imposed by high levels of physical activity superimposed on energy and sleep restriction and is more closely associated with losses in body mass and fat-free mass than other conventional nutritional biomarkers. somatotrophic hormones; military operation stress; nutritional biomarkers; soldier CIRCULATING INSULIN-LIKE GROWTH factor (IGF)-I is a liverderived 7.6-kDa polypeptide that plays a pivotal role in mediating metabolic, mitogenic, and anabolic cellular responses during altered energy states (1-3, 28). Due to its short half-life (2-4 h), specific and sensitive decline during negative energy balance (12,15,24,30) and protein-energy malnutrition (6,11,13,15,27), somatotrophic influences on body composition, and role in modulating the growth-promoting effect of physical activity, circulating IGF

Serum Sex Hormone–Binding Globulin and Cortisol Concentrations are Associated With Overreaching During Strenuous Military Training

“…Furthermore, basal serum cortisol decreased with a concomitant increase in the number of subjects who felt overloaded. Previously, serum total testosterone concentration has been shown to decrease in response to demanding training periods (6,37), as well as during extremely stressful military training periods (25,26), and to increase with overload training (36). In contrast to the present study, basal SHBG has been found to increase (19,23) and IGF-1 to decrease (23-26) after heavy training.…”

“…In particular, a diminished response of cortisol to an acute submaximal exercise (39), and reduced basal cortisol levels (31,37) may be useful indicators of exhaustive training loads. In addition, insulin-like growth hormone (IGF-1) has recently been identified as a suitable marker for monitoring training load (26) and investigating OTS. Furthermore, an impaired mood state and subjective complaints are consistently described as sensitive and early markers of OTS (37).…”

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.…”

“…Reductions in T3, IGF-1 and testosterone have been reported in field studies in male soldiers exposed to various levels of energy deficiency during military training (Friedl et al, 2000;Kyrolainen et al, 2008;Nindl et al, 2007), which suggests that key metabolic hormones may also be suppressed in severely energy-deficient exercising men. However, male reproduction requires considerably less energy than that of females (Bronson, 1985), and it is likely that the impact of low energy availability on endocrine function, and particularly reproductive function, is less pronounced in men.…”

Growth and Vascular Remodeling Factors during a Basketball Season in Adolescent Boys

“…an increase in BMI and decrease in % body fat, which indicate an increase in fat-free mass and may be associated with the IGF-1 responses to basketball training. A relationship between circulating IGF-1 and body composition alterations has been proposed, as well as the possibility this growth factor to refl ect metabolic stress and anabolic adaptations [30], such as increases in fat-free mass during exercise training [6] and particularly in young adults [30]. Exercise training may result in increased IGF-1 production both in skeletal muscle and liver, if the substantial increase in tissue metabolism and protein demands associated with training are met [31].…”