Increased gastrointestinal permeability (GP) induced by prolonged physical stress may contribute to systemic inflammation by facilitating translocation of microbial compounds from the gut. Though undernutrition and macronutrient intake independently modulate GP, relationships between diet and GP during prolonged physical stress are not well characterized. To examine the effects of energy and macronutrient intakes on GP during prolonged physical stress, 73 soldiers (71M/2F, 20 ± 1 yr, BMI 23 ± 2 kg/m 2 [ M ± SD]) were provided 3 combat rations/d, or 3 rations/d supplemented with 1000 kcal/d from protein‐ or carbohydrate‐based snacks during a 4‐d, 51 km cross‐country ski march (SKI). Energy intake was measured using ration‐specific checklists, and daily energy expenditure was measured in a subset (n = 41) by doubly‐labeled water. GP was measured in a subset (n = 48) over 24 hr before and again during SKI by dual sugar (sucralose and mannitol) absorption test. Plasma lipopolysaccharide (LPS) and serum IL‐6 were measured immediately before and after SKI as markers of microbial translocation and inflammation, respectively. Energy expenditure during SKI averaged 6179 ± 670 kcal/d. Energy deficit during SKI averaged 55 ± 12% in the combined cohort and was associated with a 2.8 ± 1.2 kg weight loss. GP increased 48 ± 7% (P < 0.001) during SKI independent of diet group (P = 0.96), and was positively associated with changes in LPS (r = 0.31, P = 0.04). Individuals with increased LPS experienced greater increases in IL‐6 relative to individuals with decreased LPS (P‐interaction = 0.07). Energy (r = −0.29), fat (r = −0.34), and carbohydrate (r = −0.31) intakes were associated with changes in GP (P ≤ 0.05), whereas the magnitude of energy deficit (r = 0.05, P = 0.79) and protein intake (r = −0.06, P = 0.67) were not. Associations between macronutrient intake and changes in GP were not significant when adjusted for total energy intake. Although correlative, these findings are consistent with microbial translocation concurrent to increased GP contributing to the inflammation induced by prolonged physical stress. Low energy intake, independent of the magnitude of energy deficit or dietary macronutrient composition, may potentiate increases in GP during periods of high energetic demand. Support or Funding Information Funded by US Army Medical Research and Material Command, and the Norwegian Defense Research Establishment agreement NO. W81XWH‐12‐0279.
Physically intense military training may diminish whole‐body protein retention and increase dietary protein requirements. This study characterized the effects of military training on whole‐body protein turnover in 21 Soldiers participating in a 7‐day winter training exercise that culminated in a 3‐day, 54 km ski march. Energy expenditure was assessed during training using doubly labeled water (D 2 18 O), and protein turnover, synthesis, breakdown, and net balance were measured at baseline (BL), day 4 (PRE, prior to the ski march), and day 7 (POST, following the ski march) using 15 N‐glycine. Energy (kcal·d ‐1 ) intake increased ( P < 0.05) PRE ([mean ± SD] 3115 ± 437) to POST (3415 ± 977), while protein (g·kg ‐1 ·d ‐1 ) intake remained constant (PRE, 1.6 ± 0.4; and POST, 1.7 ± 0.5). Although energy expenditure (kcal·d ‐1 ) increased ( P < 0.05) PRE (5171 ± 485) to POST (7190 ± 600), turnover remained steady during training (group mean ± SD, 1.4 ± 0.3 g·N ‐1 ·kg ‐1 ·d ‐1 ). Synthesis and breakdown were not influenced ( P > 0.05) by training. Net balance (g·kg ‐1 ·d ‐1 ) was maintained, as levels were similar ( P > 0.05) between BL (0.04 ± 0.3), PRE (0.01 ± 0.5), and POST (‐0.4 ± 1.0). Despite high energy expenditure and resultant energy deficit, whole‐body protein was conserved. These data suggest that protein requirements during short‐term, metabolically demanding military training are likely twice the recommended dietary allowance. Grant Funding Source : Supported by USAMRMC and FFI
BACKGROUND: Energy deficit severity is the strongest predictor of diminished whole-body protein retention during strenuous military training. Whether endogenous protein is spared by providing low-volume energy-dense foods that may promote energy intake to reduce energy deficit, or dietary protein rich in essential amino acids (EAA) to support anabolism is unknown. PURPOSE: To determine the effect of energy-dense or EAA-enriched supplemental nutrition on whole-body protein balance during strenuous military training. METHODS: Soldiers participating in 8 days of winter training were randomized to receive four supplemental bars (~375 kcal) that were either high-fat energy-dense (EN-DENSE: 34 g fat, 6.7 kcal/g, n = 22), EAA-enriched (EAA: 31 g protein, 21 g EAA, 4.2 kcal/g, n = 27) or high-carbohydrate low-energy-dense controls (CON: 70 g carbohydrate, 3.4 kcal/g, n = 19) in addition to three combat rations daily. Soldiers were instructed to eat all supplemental bars provided and consume rations ad libitum. Energy expenditure (D218O) and energy 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 15N-Alanine and total N enrichment. RESULTS: Energy expenditure (5341 ± 674 kcal/d), energy intake (4045 ± 738 kcal/d), energy deficit (-1257 ± 599 kcal/d; 24 ± 11% total energy requirements) and percent of rations (71 ± 14%) and bars (75 ± 25%) consumed did not differ (P > 0.05) between groups. Macronutrient distribution (% kcals from carbohydrate, fat, and protein) differed (P < 0.0001) between EN-DENSE (42%, 46%, 12%), EAA (45%, 35%, 20%) and CON (58%, 28%, 14%). Increases in protein flux (1.21 ± 0.23 vs. 1.29 ± 0.23 gN/kg/d; P = 0.01), PS (3.52 ± 2.01 vs. 5.05 ± 1.71 g/kg/d; P < 0.0001) and NB (-2.75 ± 1.58 vs. -1.57 ± 1.41 g/kg/d; P < 0.0001) from PRE to POST did not differ between groups. PB was unchanged from PRE to POST (6.28 ± 1.36 vs. 6.62 ± 1.38, P = 0.09). CONCLUSION: Increases in whole-body NB with strenuous military training were not different between groups, suggesting high-fat energy-dense and EAA-enriched diets do not spare endogenous protein compared with diets high in carbohydrates when total energy intake is high enough to limit energy deficits to moderate (< 40%) levels. Supported by DHP JPC-5.
Soldiers often experience severe energy deficits during military operations that diminish whole-body protein balance, even when dietary protein is consumed within recommended levels (1.5-2.0 g·kg-1·d-1). PURPOSE: To determine whether increasing total protein intake above current recommendations or increasing energy intake equally mitigate protein loss during energy deficit. METHODS: 73 Norwegian Soldiers participating in a 4-d arctic military training program (AMT, 51 kM ski march) were randomized to one of three dietary groups; control (CON; n = 18, 3 combat rations per day), protein (PRO; n = 28, 3 rations plus 4, 20 g protein, 250 kcal protein-based snack bars per day), and carbohydrate (CHO; n = 27, 3 rations plus 4, 48 g carbohydrate, 250 kcal carbohydrate-based snack bars per day). METHODS: Energy expenditure (D218O) and energy intake were measured daily. Nitrogen balance (NBAL) and whole-body protein turnover were determined at baseline (BL) and on day 3 of AMT using 24 h urine collections and [15N]-glycine. RESULTS: Protein and carbohydrate intake were highest (P < 0.05) for PRO (mean ± SE, 2.0 ± 0.1 g·kg-1·d-1) and CHO (5.8 ± 0.3 g·kg-1·d-1) but only CHO (3131 ± 122 kcal·d-1) statistically increased (P < 0.05) energy intake above CON (2506 ± 99kcal·d-1). Energy expenditure (6155 ± 60 kcal·d-1) and energy deficit (3313 ± 93 kcal·d-1) were similar across groups. Whole-body net protein balance (-0.24 ± 0.11 g·d-1) and NBAL (-77.1 ± 10.9 mg·kg-1·d-1) were negative at the conclusion of AMT in all groups. In a combined cohort, consuming more energy was associated with higher (P < 0.05) net protein balance (r = 0.57) and NBAL (r = 0.60), independent of macronutrient intake. Soldiers consuming the most energy (3754 ± 94 kcal·d-1) also consumed more (P < 0.05) protein (2.1 ± 0.1 g·kg-1·d-1) and carbohydrate (6.6 ± 0.3 g·kg-1·d-1) than those who consumed the least amount of energy (1783 ± 113 kcal·d-1, 1.2 ± 0.1 g protein·kg-1·d-1 and 3.3 ± 0.3 g carbohydrate·kg-1·d-1), and 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 negative consequences of the energy deficit and attenuate whole-body protein loss. Funding Supported by MRMC and FFI
Load carriage (LC) exercise may exacerbate inflammation during training. Nutritional supplementation may mitigate this response by sparing endogenous carbohydrate stores, enhancing glycogen repletion, and attenuating negative energy balance. Two studies were conducted to assess inflammatory responses to acute LC and training, with or without nutritional supplementation. Study 1: 40 adults fed eucaloric diets performed 90-min of either LC (treadmill, mean ± SD 24 ± 3 kg LC) or cycle ergometry (CE) matched for intensity (2.2 ± 0.1 VO2peak L min−1) during which combined 10 g protein/46 g carbohydrate (223 kcal) or non-nutritive (22 kcal) control drinks were consumed. Study 2: 73 Soldiers received either combat rations alone or supplemented with 1000 kcal day−1 from 20 g protein- or 48 g carbohydrate-based bars during a 4-day, 51 km ski march (~45 kg LC, energy expenditure 6155 ± 515 kcal day−1 and intake 2866 ± 616 kcal day−1). IL-6, hepcidin, and ferritin were measured at baseline, 3-h post exercise (PE), 24-h PE, 48-h PE, and 72-h PE in study 1, and before (PRE) and after (POST) the 4-d ski march in study 2. Study 1: IL-6 was higher 3-h and 24-h post exercise (PE) for CE only (mode × time, P < 0.05), hepcidin increased 3-h PE and recovered by 48-h, and ferritin peaked 24-h and remained elevated 72-h PE (P < 0.05), regardless of mode and diet. Study 2: IL-6, hepcidin and ferritin were higher (P < 0.05) after training, regardless of group assignment. Energy expenditure (r = 0.40), intake (r = −0.26), and balance (r = −0.43) were associated (P < 0.05) with hepcidin after training. Inflammation after acute LC and CE was similar and not affected by supplemental nutrition during energy balance. The magnitude of hepcidin response was inversely related to energy balance suggesting that eating enough to balance energy expenditure might attenuate the inflammatory response to military training.
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).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.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.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.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.
