Improving Dietary Protein Quality Reduces the Negative Effects of Physical Inactivity on Body Composition and Muscle Function

Abstract

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. 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. 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). 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.