Prolonged high altitude exposure exacerbates fat‐free mass and fat mass loss during negative energy balance regardless of dietary protein intake

Abstract

Protein intake above the recommended dietary allowance attenuates fat‐free mass (FFM) loss during moderate negative energy balance (~40% energy deficit) at sea level (SL). Sustained periods of strenuous physical activity at high altitude (HA) may exacerbate FFM loss, especially during energy deficit. However, increased dietary protein intake has not been evaluated as a countermeasure to FFM loss at HA. This study aimed to determine whether consuming dietary protein at amounts consistent with current recommendations for elevated physical activity (2.0 g protein/kg) attenuates FFM loss during prolonged energy deficit at HA. Seventeen healthy males (mean ± SD, 23.4 ± 5.6y, 81.9± 13.9 kg) participated in a 2‐phase, 43‐d study. During phase 1 (SL), participants were instructed to consume a weight maintenance diet with standard protein intake(1.0 g protein/kg, STD) for 21 d. During phase 2, participants resided at HA (4300 m, Pikes Peak, CO) for 22 d and were randomly assigned to either a STD or high (2.0 g protein/kg, HIGH) protein diet designed to elicit a 40% energy deficit (30% dietary restriction and 10% increase in physical activity, estimated energy deficit was 1074 ± 122 kcal/d based on the total energy requirements necessary to maintain body mass during phase 1) and~3 kg total body mass loss. Diet and physical activity were highly controlled. Total body mass, FFM, and fat mass (FM) were assessed by dual energy x‐ray absorptiometry and resting metabolic rate (RMR) by indirect calorimetry. Volunteers were weight stable during SL and lost −7.9 ± 1.9 kg(P<0.01)during HA, regardless of protein group (P>0.05). Decrements in FFM (−4.0 ± 3.3 vs. −3.2 ± 1.5 kg) and FM (−3.3 ± 1.8 vs. −3.9 ± 0.8 kg) were not statistically different between STD and HIGH (P>0.05). The overall energy deficit was 2306 ± 444kcal/d when calculated based on changes in FFM and FM. The additional energy deficit was attributable, in part, to an increase in RMR, which peaked at 58%above SL on HA day 1 and remained ≥ 25% higher than SL throughout HA(P<0.05), accounting for 27% (634 ± 273 kcal/d) of the total energy deficit at HA. The remaining 598 kcal/d (26% of total deficit) could not be accounted for by estimated energy expenditure of prescribed daily physical activity and measured energy intake, suggesting the energy cost of physical activity may be greater at HA than SL. Prolonged HA exposure exacerbated the catabolic effects of negative energy balance. In this context, consuming a higher versus standard protein diet was equally ineffective at sparing FFM with weight loss. The opinions or assertions contained herein are the private views of the author(s)and are not to be construed as official or reflecting the views of the Army or the Department of Defense.Support or Funding InformationSupported by USAMRMC.