Initial Military Training Modulates The Serum Metabolome

Abstract

PURPOSE: Initial military training (IMT) affects body composition by increasing lean mass and decreasing fat mass. The underlying metabolic adaptations associated with changes in body composition during IMT are unknown. Metabolomics analysis provides a comprehensive understanding of metabolic adaptations, which may yield mechanistic insight regarding these body composition changes. This study aimed to assess changes in body composition and the serum metabolome during IMT. METHODS: Data collection was conducted before (PRE) and after (POST) 22-week US Army IMT at Ft. Benning, GA. Fifty-four volunteers (mean±SD; 22 ± 3y; 24.6 ± 3.7 kg/m2) completed this longitudinal study. Body composition measurements (InBody 770, Cerritos, CA) and blood samples were collected under fasting, rested conditions PRE and POST IMT. Global metabolite profiling was performed to identify metabolites involved in energy, carbohydrate, lipid, and protein metabolism (Metabolon, Inc.). Paired t tests were used to determine differences between PRE and POST measures (P < 0.05). False discovery was controlled using the Benjamini Hochberg method. RESULTS: Body mass was maintained (mean difference ± SD, 0.4 ± 5.1, P > 0.05), fat mass was reduced (-1.7 ± 3.5 kg, P < 0.01), and lean mass was increased (2.1 ± 2.8 kg, P < 0.01) at POST compared to PRE. Of 682 identified metabolites, 367 differed at POST compared to PRE (P < 0.05, Q < 0.10). The majority of these metabolites were related to fatty acid (69%) and amino acid (23%) metabolism. Decreases were detected in 93% of long chain fatty acid metabolites, while 67% of primary bile acid metabolites increased. Increases were also detected in 52% of branched chain amino acid metabolites, 65% of histidine metabolites, and 40% of urea cycle metabolites. CONCLUSIONS: Changes in fatty acid metabolites indicate increased fat oxidation, consistent with reductions in fat mass observed during IMT. Increases in amino acid metabolites suggest higher rates of amino acid and nitrogen turnover, which may contribute to increases in fat free mass during IMT. Overall, changes in metabolomics profiles provide potential mechanistic insight into metabolic adaptions underlying changes in body composition during IMT.