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.