Sex Does Not Affect Changes in Body Composition and Insulin-Like Growth Factor-I During US Army Basic Combat Training

Abstract

Roberts, BM, Staab, JS, Caldwell, AR, Sczuroski, CE, Staab, JE, Lutz, LJ, Reynoso, M, Geddis, AV, Taylor, KM, Guerriere, KI, Walker, LA, Hughes, JM, and Foulis, SA. Sex does not affect changes in body composition and insulin-like growth factor-I during US army basic combat training. J Strength Cond Res XX(X): 000-000, 2023-Insulin-like growth factor 1 (IGF-I) has been implicated as a biomarker of health and body composition. However, whether changes in body composition are associated with changes in IGF-I is unclear. Therefore, we examined the relationship between body composition changes (i.e., fat mass and lean mass) and total serum IGF-I levels in a large cohort of young men (n = 809) and women (n = 397) attending US Army basic combat training (BCT). We measured body composition using dual energy x-ray absorptiometry and total serum IGF-I levels during week 1 and week 9 of BCT. We found that pre-BCT lean mass (r = 0.0504, p = 0.082) and fat mass (r = 0.0458, p = 0.082) were not associated with pre-BCT IGF-I. Body mass, body mass index, body fat percentage, and fat mass decreased, and lean mass increased during BCT (all p < 0.001). Mean (±SD) IGF-I increased from pre-BCT (176 ± 50 ng·ml-1) to post-BCT (200 ± 50 ng·ml-1, p < 0.001). Inspection of the partial correlations indicated that even when considering the unique contributions of other variables, increases in IGF-I during BCT were associated with both increased lean mass (r = 0.0769, p = 0.023) and increased fat mass (r = 0.1055, p < 0.001) with no sex differences. Taken together, our data suggest that although changes in IGF-I weakly correlated with changes in body composition, IGF-I, in isolation, is not an adequate biomarker for predicting changes in body composition during BCT in US Army trainees.