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.
Highlights
Military operations commonly require prolonged physical exertion in austere environments resulting in high energy expenditures that are generally not matched by increases in energy intake (Friedl et al 1994, 2000; Tharion et al 2005; Margolis et al 2013, 2014)
The major finding of this study was that a multistressor military training environment characterized by high physical activity and a short-term but severe energy deficit elicited pronounced changes in plasma metabolite profiles that were consistent with an increase in energy metabolism, lipolysis, fatty acid oxidation, and ketogenesis
Changes in metabolites related to lipolysis and fatty acid oxidation were correlated with body mass loss and energy balance during training, whereas changes in metabolite levels were generally not correlated with energy expenditure, energy intake, or macronutrient intakes
Summary
Military operations commonly require prolonged physical exertion in austere environments resulting in high energy expenditures that are generally not matched by increases in energy intake (Friedl et al 1994, 2000; Tharion et al 2005; Margolis et al 2013, 2014). This provides opportunities for studying the range of human physiologic responses to severe energy deficit in combination with multiple additional stressors (e.g., sleep deprivation, psychological stress).
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