Improving dietary protein quality reduces the negative effects of physical inactivity on body composition and muscle function

Background: Brief periods of physical inactivity can compromise muscle health. Increasing dietary protein intake is potentially beneficial but complicated by difficulties reconciling anabolic potential with a realistic food volume and energy intake. We sought to determine whether increasing dietary protein quality could reduce the negative effects of physical inactivity. Methods: Twenty healthy, older men and women completed 7 days of bed rest followed by 5 days of rehabilitation. Volunteers consumed a mixed macronutrient diet (MIXED: N = 10; 68 ± 2 years; 1,722 ± 29 kcal/day; 0.97 ± 0.01 g protein/kg/day) or an isoenergetic, whey-augmented, higher protein quality diet (WHEY: N = 10; 69 ± 1 years; 1,706 ± 23 kcal/day; 0.90 ± 0.01 g protein/kg/day). Outcomes included body composition, blood glucose, insulin, and a battery of physical function tests. Results: During bed rest, both groups experienced a 20% reduction in knee extension peak torque (p < .05). The WHEY diet partially protected leg lean mass (−1,035 vs. −680 ± 138 g, MIXED vs. WHEY; p = .08) and contributed to a greater loss of body fat (−90 vs. −233 ± 152 g, MIXED vs. WHEY; p < .05). Following rehabilitation, knee extension peak torque in the WHEY group fully recovered (−10.0 vs. 2.2 ± 4.1 Nm, MIXED vs. WHEY; p = .05). Blood glucose, insulin, aerobic capacity, and Short Physical Performance Battery (SPPB) changes were similar in both dietary conditions (p > .05). Conclusions: Improving protein quality without increasing total energy intake has the potential to partially counter some of the negative effects of bed rest in older adults.