Protein Yogurt Matches Whey for Muscle Gains in Older Adults While Boosting Gut Health

Sarcopenia—the progressive, age-related loss of muscle mass and strength—is a major driver of functional decline in older adults. While strength training (ST) is the cornerstone intervention, adequate protein intake amplifies anabolic responses. Whey protein isolate (WPI) dominates the supplement market, but questions remain about whether whole-food protein sources like high-protein yogurt can deliver comparable musculoskeletal benefits, and whether they differ in their effects on the gut microbiome, itself increasingly implicated in sarcopenia pathology.

This randomized controlled trial enrolled 17 inactive adults aged 60–70 years, assigning them to consume either 25 g of whey protein (WP) or 24.5 g of protein from high-protein yogurt (PY) immediately post-training during an 8-week supervised ST program (3 sessions/week, 70–85% of 10RM). Assessments at baseline and 8 weeks included body composition via bioelectrical impedance analysis (BIA), muscle strength (10RM, isokinetic torque, handgrip), gait speed, resting metabolic rate (RMR), and gut microbiome composition via 16S rRNA sequencing. Repeated-measures ANOVA and standard alpha/beta diversity metrics were applied.

Both groups achieved statistically equivalent gains in skeletal muscle mass (WP: +0.47 kg; PY: +0.50 kg) and showed significant improvements in strength across all measures and gait speed (p < 0.01), with no between-group differences. A notable divergence emerged in secondary outcomes: fat mass decreased significantly only in the WP group (p = 0.02), while resting metabolic rate increased only in the PY group (p = 0.03). These contrasting metabolic signatures may reflect differences in fermentation byproducts, the probiotic matrix of yogurt, and the slower casein-dominant digestion kinetics of dairy.

Microbiome analysis produced the study's most striking divergence. Whey protein increased the Firmicutes/Bacteroidota ratio and selectively enriched Subdoligranulum, a butyrate-producing genus associated with inflammation modulation. Protein yogurt, by contrast, enhanced alpha diversity—a widely used marker of gut ecosystem resilience—and increased Coprococcus abundance, a genus linked to short-chain fatty acid production and positive metabolic health associations. Functional pathway predictions further indicated differential enrichment in metabolic and signaling processes between groups. These findings align with the known prebiotic and probiotic properties of fermented dairy and suggest that the food matrix surrounding protein, not just protein quantity, shapes microbiome outcomes.

The clinical implications are meaningful: high-protein yogurt appears to be a nutritionally equivalent, more affordable, and potentially gut-health-superior alternative to whey protein supplements for older adults engaging in structured resistance training. Given that gut dysbiosis is increasingly recognized as a contributor to sarcopenia, the yogurt-associated improvements in microbiome diversity may provide compounding long-term benefits beyond muscle mass alone. Limitations include the small sample size (n = 17), short intervention duration (8 weeks), and lack of a no-protein control group, which prevent definitive causal conclusions about microbiome-muscle interactions.