Effects of Supplemental Energy on Protein Balance during 4-d Arctic Military Training

Abstract

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[middle dot]kg-1[middle dot]d-1).

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 (D218O) 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 [15N]-glycine.

Results: Protein and carbohydrate intakes were highest (P < 0.05) for PRO (mean +/- SD, 2.0 +/- 0.3 g[middle dot]kg-1[middle dot]d-1) and CHO (5.8 +/- 1.3 g[middle dot]kg-1[middle dot]d-1), but only CHO increased (P < 0.05) energy intake above CON. Energy expenditure (6155 +/- 515 kcal[middle dot]d-1), energy balance (-3313 +/- 776 kcal[middle dot]d-1), net protein balance (NET) (-0.24 +/- 0.60 g[middle dot]d-1), and NBAL (-68.5 +/- 94.6 mg[middle dot]kg-1[middle dot]d-1) 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[middle dot]d-1, 2.11 +/- 0.45 g protein[middle dot]kg-1[middle dot]d-1, 6.654 +/- 1.16 g carbohydrate[middle dot]kg-1[middle dot]d-1) 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.