Military training elicits marked increases in plasma metabolomic signatures of energy metabolism, lipolysis, fatty acid oxidation, and ketogenesis

TLDR

Military training studies reveal how extreme physiologic stress and nutrition influence metabolic responses, and metabolomics offers new tools to deepen this understanding. The study aimed to investigate whole‑body metabolic changes during strenuous military training in relation to energy balance and macronutrient intake. Researchers performed nontargeted global metabolite profiling on plasma from 25 male soldiers before and after a 4‑day, 51‑km cross‑country ski march that produced high energy expenditure and severe deficits. During the march, 478 of 737 plasma metabolites altered, with widespread increases in free fatty acids and acylcarnitines, decreases in mono‑ and diacylglycerols, modest rises in TCA cycle intermediates and branched‑chain amino acids, and these lipid‑metabolism shifts correlated with body‑mass loss and energy deficit rather than intake or expenditure, indicating heightened energy metabolism, lipolysis, fatty‑acid oxidation, ketogenesis, and BCAA catabolism driven by the magnitude of the energy deficit.

Abstract

Military training studies provide unique insight into metabolic responses to extreme physiologic stress induced by multiple stressor environments, and the impacts of nutrition in mediating these responses. Advances in metabolomics have provided new approaches for extending current understanding of factors modulating dynamic metabolic responses in these environments. In this study, whole-body metabolic responses to strenuous military training were explored in relation to energy balance and macronutrient intake by performing nontargeted global metabolite profiling on plasma collected from 25 male soldiers before and after completing a 4-day, 51-km cross-country ski march that produced high total daily energy expenditures (25.4 MJ/day [SD 2.3]) and severe energy deficits (13.6 MJ/day [SD 2.5]). Of 737 identified metabolites, 478 changed during the training. Increases in 88% of the free fatty acids and 91% of the acylcarnitines, and decreases in 88% of the mono- and diacylglycerols detected within lipid metabolism pathways were observed. Smaller increases in 75% of the tricarboxylic acid cycle intermediates, and 50% of the branched-chain amino acid metabolites detected were also observed. Changes in multiple metabolites related to lipid metabolism were correlated with body mass loss and energy balance, but not with energy and macronutrient intakes or energy expenditure. These findings are consistent with an increase in energy metabolism, lipolysis, fatty acid oxidation, ketogenesis, and branched-chain amino acid catabolism during strenuous military training. The magnitude of the energy deficit induced by undereating relative to high energy expenditure, rather than macronutrient intake, appeared to drive these changes, particularly within lipid metabolism pathways.