Whole-Body Protein Balance during Arctic Military Training Is Unaffected by Dietary Essential Amino Acid or Energy Density

Energy deficit severity and dietary protein intake are primary determinants of negative whole-body protein balance during strenuous military training. This work aimed to determine whether attenuating energy deficits by providing low-volume energy-dense foods that may promote energy intake or consuming essential amino acid (EAA)-dense foods to facilitate an anabolic state, preserves whole-body protein balance during strenuous cold-weather military training. This randomized, controlled trial enrolled Norwegian soldiers participating in an 8-day Arctic training exercise. Participants were randomized to three groups that received three standard rations plus four supplemental bars that were EAA-dense (EAA-Dense; n=27), energy-dense (EN-Dense; n=22), or high-carbohydrate controls (CON; n=19) each day. Energy expenditure (doubly labeled water) and dietary intake were measured daily. Whole-body protein flux, synthesis (PS), breakdown (PB), and net balance (NB=PS–PB) were measured overnight before (PRE) and after the training (POST) using 15 N-Alanine. Energy expenditure (5341 ± 674 kcal·d -1 ), energy intake (4045 ± 738 kcal·d -1 ), and energy deficits (-1257 ± 599 kcal·d -1 ; 24 ± 11%) were not different ( P > 0.05) between groups. Protein intake was above 1.6 g·kg -1 ·d -1 in all treatments. Protein flux (1.21 ± 0.23 vs. 1.34 ± 0.36 g N·kg -1 ·d -1 ), PS (3.46 ± 2.06 vs. 5.43 ± 2.86 g·kg -1 ·d -1 ), PB (6.26 ± 1.35 vs. 6.95 ± 2.12 g·kg -1 ·d -1 ) and NB (-2.80 ± 1.61 vs. -1.51 ± 1.60 g·kg -1 ·d -1 ) increased ( P < 0.05) from PRE to POST, independent of treatment. Soldiers achieved high protein intakes and modest energy deficits when provided three standard rations and four supplemental bars daily during cold-weather training. Supplemental bar energy- or EAA-density did not affect whole-body protein balance under these conditions, suggesting protein utilization remains independent of the macronutrient formulation of supplemental bars during military training scenarios with high protein intakes and moderate energy deficits. This trial was registered at clinicaltrials.gov (NCT05210205). This trial was registered at www.clinicaltrials.gov as NCT05210205. https://clinicaltrials.gov/study/NCT05210205