Changes in Protein Turnover, Hormonal Status, and Body Composition during Physiologically Demanding Military Training

Abstract

Physiological stress imposed during short‐term military training is often severe and intentional; producing a catabolic state and loss of lean body mass (LBM). The extent to which this occurs and metabolic responses that may contribute to the loss of LBM are not well characterized. This study examined body composition, whole‐body protein turnover (15N‐alanine), testosterone and cortisol before (BASELINE) and after (POST) 7 days of Survival, Evasion, Resistance, and Escape (SERE) School in 68 male US Marines (mean ± SD, 25 ± 2 y, 83.7 ± 9.1 kg). Total body mass (TBM) was 7% lower (−2.7 ± 1.4 kg fat and −3.1 ± 1.7 kg LBM), proteolysis 28% higher and net protein balance 132% lower POST‐SERE (P < 0.05) compared to BASELINE. Decrements in testosterone POST‐SERE (−42%; −221 ± 136 ng/dL; P < 0.05) were inversely related with increased proteolysis (r = −0.30; P < 0.05) and protein synthesis (r = −0.28; P < 0.05). Percent changes in testosterone were associated with percent loss of TBM (r = 0.37; P < 0.05) and LBM (r = 0.31; P < 0.05). Cortisol changes during SERE were associated with changes in protein synthesis (r = 0.26; P < 0.05). Percent change in cortisol was inversely associated with percent change in fat mass (r = −0.34, P < 0.05) and tended to predict the percent change in LBM (r = 0.22; P = 0.07). The physiological stress during SERE elicits a hypogonadal state and catabolism of LBM. Decrements in testosterone were quantitatively associated with the increase in proteolysis and loss of LBM.Support or Funding InformationSupported by USAMRMC