Background: Adopting a plant-based diet may compromise protein intake and impair skeletal muscle mass in older adults.
Objectives: To compare the impact of a 12-week self-selected vegan diet to an omnivorous diet, and a self-selected vegan diet with resistance exercise (RE) on muscle mass, strength and muscle protein synthesis (MPS) rates in older adults.
Methods: This randomized controlled trial included 3 parallel study arms in which 72 healthy older adults aged ≥65y were randomly assigned to follow 1) a self-selected vegan diet (VEG), 2) their habitual omnivorous diet (OMNI), or 3) a self-selected vegan diet with RE (VEG-RE). At baseline and after 12 weeks, thigh muscle volume, thigh muscle fat infiltration, and body fat distribution were assessed using magnetic resonance imaging, appendicular lean mass with dual X-ray absorptiometry, and muscle strength via Biodex. MPS rates were assessed during the first 10 days using a deuterium oxide protocol. Other outcome measures were body mass, dietary intake, and physical activity. Linear mixed models were applied to test differences between VEG and the other groups. Results are presented as estimated marginal mean or change in estimated marginal mean (95%CI).
Results: VEG reduced protein intake with -27.7(-37.3,-18.2), -22.0(-31.7, -12.4), and -19.3(-29.2,-9.37) g/day in week 1, 6 and 12 (all P<0.0001 compared with baseline), which was similar to the decrease in VEG-RE (P>0.05), but different from OMNI (P<0.0001), in which protein intake did not change. Thigh muscle volume and appendicular lean mass significantly reduced in VEG (-0.61(-0.72,-0.50)L; -1.15(-1.46,-0.85)kg) compared to OMNI (-0.01(-0.11,0.09)L; +0.05(-0.23,0.32)kg; both P<0.0001) and VEG-RE (-0.35(-0.47,-0.24)L, P=0.0038; -0.62(-0.93,-0.32)kg, P=0.0033). MPS was lower in VEG (1.09(1.01,1.17)%/day) compared with OMNI (1.27(1.18,1.35)%/day); P=0.0073) and VEG-RE (1.24(1.16,1.33)%/day; P=0.0246).
Conclusions: A self-selected vegan diet reduces protein intake, skeletal muscle mass and MPS in older adults. The negative impact of a vegan diet on skeletal muscle mass can be mitigated by RE.