In a 12-week randomized non-inferiority trial of 108 adults averaging 66 years old, both a lacto-ovo vegetarian and an omnivorous diet combined with three weekly resistance training sessions produced significant appendicular muscle mass gains — +0.38 kg and +0.66 kg respectively. Leg press strength, chair stand performance, and handgrip strength improved in both groups with no statistically significant between-group differences. However, non-inferiority was not established: vegetarians consumed 0.33 g/kg/day less protein (1.24 vs 1.58 g/kg/day), and the muscle mass gap of 0.33 kg exceeded the predefined non-inferiority margin of 0.25 kg.
This trial adds important nuance to the plant-protein debate for aging adults. The 0.28 kg difference in muscle gain is modest in absolute terms but clinically meaningful for sarcopenia prevention in older populations, where every fraction of lean mass counts for fall risk and functional independence. Crucially, both groups cleared the 1.2 g/kg/day protein threshold widely recommended for older exercisers — suggesting the vegetarian shortfall was relative, not absolute. The finding challenges a common assumption that plant-based eating is incompatible with muscle preservation in older adults, while simultaneously cautioning that effortful dietary planning is required. Limitations include the self-selected food design (real-world strength but less experimental control), a short 12-week window, and the absence of individual amino acid profiling — leucine adequacy, not just total protein, may drive differential anabolic responses. Overall, a well-designed, confirmatory-plus-nuancing contribution to the field.