Effects of daily intake of cacao polyphenols, alone or with milk protein, on skeletal muscle mass in community-dwelling older adults: an exploratory 16-week randomized, open-label, parallel-group trial

Abstract Background Evidence on food-based strategies to maintain muscle-related body composition in older adults under habitual lifestyle conditions is limited. Cacao flavanols may influence vascular and redox pathways, whereas milk protein provides amino acids relevant to muscle protein synthesis. We examined whether daily high-cacao chocolate, alone or with a protein-enriched milk beverage, affected body composition in community-dwelling older adults. Methods This exploratory 16-week randomized, open-label, parallel-group trial included adults aged 60–79 years. Participants were allocated 1:1:1 to no intake (NI), high-cacao chocolate (HC; 15 g/day), or HC plus a protein-enriched milk beverage (HC+MILK; 200 mL/day). Body composition was assessed by multifrequency bioelectrical impedance analysis (BIA) at baseline, week 8, and week 16. Longitudinal models evaluated observed values and changes from baseline, and pairwise comparisons were adjusted using Tukey’s method. The per-protocol set was the primary efficacy population. Results Of 240 randomized participants, 219 were included in the per-protocol set (NI, 76; HC, 72; HC+MILK, 71). At week 16, soft lean mass changed by − 0.24, + 0.21, and + 0.25 kg in NI, HC, and HC+MILK, respectively. Compared with NI, the change was + 0.45 kg with HC (95% CI 0.06 to 0.83; P = 0.015) and + 0.49 kg with HC+MILK (0.10 to 0.88; P = 0.005). Fat-free mass, skeletal muscle mass, and skeletal muscle index showed consistent significant differences versus NI, whereas HC+MILK did not differ from HC. No intervention-specific effect was observed for physical-function outcomes, and no product-related adverse events occurred. Conclusions Over 16 weeks, HC and HC+MILK showed statistically significant favorable changes in BIA-derived muscle-related indices compared with NI, without a clear incremental benefit of adding MILK. These findings suggest a potential benefit for maintaining BIA-estimated muscle mass under habitual activity conditions, although the clinical relevance remains uncertain because no intervention-specific functional benefit was detected and changes in exercise type and intensity were not assessed comprehensively. Trial registration UMIN000054576 (June 6, 2024).