Effects of Supplemental Energy on Protein Balance during 4 d Arctic Military Training.
UNLABELLED Soldiers often experience negative energy balance during military operations that diminish whole body protein retention, even when dietary protein is consumed within recommended levels (1.5 2.0 g*kg*d) PURPOSE The objective of this study is to determine whether providing supplemental nutrition spares whole body protein by attenuating the level of negative energy balance induced by military training and to assess whether protein balance is differentially influenced by the macronutrient source. METHODS Soldiers participating in 4 d arctic military training (AMT) (51 km ski march) were randomized to receive three combat rations (CON) (n 18) three combat rations plus four 250 kcal protein based bars (PRO, 20 g protein) (n 28) or three combat rations plus four 250 kcal carbohydrate based bars daily (CHO, 48 g carbohydrate) (n 27) Energy expenditure (D2O) and energy intake were measured daily. Nitrogen balance (NBAL) and protein turnover were determined at baseline (BL) and day 3 of AMT using 24 h urine and [N] glycine. RESULTS Protein and carbohydrate intakes were highest (P 0.05) for PRO (mean SD, 2.0 0.3 g*kg*d) and CHO (5.8 1.3 g*kg*d) but only CHO increased (P 0.05) energy intake above CON. Energy expenditure (6155 515 kcal*d) energy balance 3313 776 kcal*d) net protein balance (NET) 0.24 0.60 g*d) and NBAL 68.5 94.6 mg*kg*d) during AMT were similar between groups. In the combined cohort, energy intake was associated (P 0.05) with NET (r 0.56) and NBAL (r 0.69) and soldiers with the highest energy intake (3723 359 kcal*d, 2.11 0.45 g protein*kg*d, 6.654 1.16 g carbohydrate*kg*d) achieved net protein balance and NBAL during AMT. CONCLUSION These data reinforce the importance of consuming sufficient energy during periods of high energy expenditure to mitigate the consequences of negative energy balance and attenuate whole body protein loss.
Medicine and science in sports and exercise