Effects of exercise mode, energy, and macronutrient interventions on inflammation during military training

Abstract

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.

Elevated Serum Hepcidin Levels during an Intensified Training Period in Well-Trained Female Long-Distance Runners

“…Second, energy expenditure during training was not assessed. Pasiakos et al reported that changes in hepcidin levels after a four-day military training regimen were related to the total daily energy expenditure [42]. Thus, 24 h energy expenditure data will be of value in determining whether lower energy availability is a predominant factor in elevated hepcidin levels during the intensified training period.…”

Nutritional interventions and the IL‐6 response to exercise

“…Circulating concentrations of IL‐6 after 90 min of recovery were ~40% lower in those who consumed the protein bar compared to the placebo bar; however, this difference was not statistically significant ( P = 0.055). In contrast, chronic consumption of protein before, during, and after eccentric exercise appears to have no effect on the IL‐6 response (69, 79, 80). Collectively, these studies suggest that consuming protein immediately after prolonged high‐intensity exercise may attenuate circulating concentrations of immune cell–derived IL‐6.…”

“…Effects of protein or amino acid supplementation on exercise‐induced IL‐6 are shown in Supplemental Table 3 (69, 73, 77–83). Kerasioti et al (77) had recreationally active men consume an experimental or isocaloric placebo cake containing varying levels of protein and carbohydrate (0.26 g protein/kg body weight/h and 0.90 g carbohydrate/kg body weight/h or 0.10 g protein/kg body weight/h and 1.1 g carbohydrate/kg body weight/h) immediately after and at 1, 2, and 3 h of recovery from 2 h of cycling at 60 to 65% VO 2max .…”

“…Studies that determined the hepcidin response to exercise are shown in Supplemental Table 6 (49, 56, 65, 67, 69, 70, 88, 96). All studies that reported an increase in circulating levels of IL‐6 after exercise also reported an increase in hepcidin (49, 56, 65, 67, 69, 70, 96). Accordingly, the postexercise increase in circulating levels of IL‐6 preceded the rise in hepcidin at ~3 h after exercise, which in some instances resulted in declines in markers of iron status.…”

“…Importantly, studies that provided mixed meals over the course of a training period or for an extended period before exercise failed to elicit an attenuation in IL-6 (68)(69)(70)(71)(72). This could suggest that adaptation to the meal may occur over time; however, these results are difficult to interpret because of the timing of the blood draw (70,73,74) and nutrition before the exercise test (71).…”