No effect of increasing protein intake during military exercise with severe energy deficit on body composition and...

In this study, we compare the effects of isocaloric high- (HIGH: 2 g kg^-1  d^-1 , n = 19) and low-protein diet (LOW: 1 g kg^-1  d^-1 , n = 19) on changes in body composition, muscle strength, and endocrine variables in response to a 10-day military field exercise with energy deficit, followed by 7 days of recovery. Body composition (DXA), one repetition maximum (1RM) bench and leg press, counter-movement jump height (CMJ) and blood variables were assessed before and after the exercise. Performance and blood variables were reassessed after 7 days of recovery. The 10-day exercise resulted in severe energy deficit in both LOW and HIGH (-4373 ± 1250, -4271 ± 1075 kcal d^-1 ) and led to decreased body mass (-6.1%, -5.2%), fat mass (-40.5%, -33.4%), 1RM bench press (-9.5%, -9.7%), 1RM leg press (-7.8%, -8.3%), and CMJ (-14.7%, -14.6%), with no differences between groups. No change was seen for fat-free mass. In both groups, the exercise led to a switch toward a catabolic physiological milieu, evident as reduced levels of anabolic hormones (testosterone, IGF-1) and increased levels of cortisol (more pronounced in HIGH, P < .05). Both groups also displayed substantial increases in creatine kinase. After 7 days of recovery, most variables had returned to close-to pre-exercise levels, except for CMJ, which remained at reduced levels. In conclusion, increased protein intake during 10-day military field exercise with severe energy deficiency did not mitigate loss of body mass or impairment of physical performance.