Longitudinal Comparison of Lean Body Mass by Dual Energy X-Ray Absorptiometry and Muscle Mass by Creatine (methyl-d3) Dilution in Response to a 28-d Severe Energy Deficit

Abstract

Abstract Objectives We reported that healthy males supplemented with testosterone gained lean body mass (LBM) during 28-d of energy deficit and 14 d of ad libitium feeding when measured by dual energy x-ray absorptiometry (DXA), but with no increase in muscle strength. We were unable to determine whether LBM gains were due to muscle mass accrual since DXA does not deliniate muscle from visceral organs and body water. Objectives: To assess the effects of testosterone supplementation on muscle mass as measured by creatine (methyl-d3) dilution, and determine the relationship between muscle mass and DXA-measured LBM in response to short-term energy deficit. Methods Secondary analysis of a 3-phase, randomised, double-blind, placebocontrolled trial in healthy males: 14-d free-living, eucaloric phase (P1); 28-d live-in, 55% energy deficit phase with (200 mg testosterone enanthate/wk, TEST, n = 24) or without (PLA, n = 26) testosterone (P2); and 14-d free-living, ad libitum feeding phase (P3). Muscle mass was measured by creatine dilution and LBM by DXA at the end of each phase. Results We previously reported increased LBM in TEST (mean change from P1 ± SEM; 2.5 ± 0.4, P < 0.01), but not PLA (−0.3 ± 0.3 kg, P > 0.05), following P2. Both TEST (5.2 ± 0.4 kg) and PLA (2.2 ± 0.4 kg) gained LBM in P3 (P < 0.01). There was a treatment-by-phase trend for change in muscle mass (P-interaction = 0.054), but muscle mass data were highly variable and no post-hoc comparisons met statistical significance (PLA, P2: −0.3 ± 1.6; TEST, P2: −0.7 ± 1.7; PLA, P3: −0.3 ± 1.6; TEST, P3: 3.8 ± 1.7 kg; P > 0.05). Cross-sectional measures of muscle mass were correlated (P < 0.001) with total and appendicular LBM at P1 (r = 0.63 and 0.67), P2 (r = 0.71 and 0.72), and P3 (r = 0.55 and 0.48), respectively. However, changes in muscle mass were not associated with changes in total or appendicular LBM at P2 or P3 (P > 0.05). Conclusions Testosterone supplementation increased LBM in response to short-term energy deficit and recovery feeding, but had no significant effect on muscle mass or muscle function. The discordance between changes in LBM and muscle mass underscore the inherent limitations of LBM as a surrogate measure for skeletal muscle mass, particularly in response to short-term intervention studies. Funding Sources DHP JPC-5/MOMRP; authors’ views not official U.S. Army or DoD policy.