ObjectiveThis study investigated the effects of a soy protein-rich meal intervention on the muscle health of older adults in long-term care facilities. MethodsA 12-week single-center randomized controlled trial with a control-group and open-label design was conducted. Eighty-four older adults from a long-term care facility participated in the study. The chefs at the facility cooked three meals using soy protein-rich recipes designed by dieticians. For 12 weeks, the intervention group participants consumed three meals with 30 g of soy protein (10 g/meal) per day, and the control group participants maintained their habitual diets. ResultsThe 84 participants (mean age, 84.9 ± 7.0 years; 61.9% female) were randomly assigned to an intervention group (43 participants) and a control group (41 participants). The intervention group exhibited significant increases in several lean mass indicators, namely soft lean mass (mean, 1.43 kg; 95% confidence interval [CI]: 0.20–1.65 kg), skeletal muscle mass (mean, 1.20 kg; 95% CI: 0.43–1.96 kg), appendicular skeletal muscle mass (mean, 0.79 kg; 95% CI: 0.07–1.52 kg), and skeletal muscle index (mean, 0.37 kg/m2; 95% CI: 0.05–0.68 kg/m2) (all P < 0.05). These changes were not observed in the control group (all P > 0.05). Notably, calf circumference decreased significantly in the control group (mean, −0.98 cm; 95% CI: −1.61 to −0.36 cm) but was maintained in the intervention group. The differences in the calf circumference and 6-m walk performance of the two groups were significant (P < 0.05). ConclusionsThe 12-week soy protein-rich meal intervention improved the muscle mass and 6-m walk performance of older adults in a long-term care facility.