Protein yogurt and whey protein produce comparable muscle gains, but divergent microbiome shifts during strength training in older adults

Sarcopenia, the age-related decline in muscle mass and strength, affects the functional capacity of older adults. Strength training (ST) combined with adequate protein intake is a key element in reversing and improving functional capacity. Protein, especially Whey Protein isolates (WPI), is widely used to improve muscle mass. In contrast, high-protein products, such as protein yogurt (PY), may offer similar benefits for muscle health and drive additional effects on gut health, which is altered in older adults. For this, we aim to compare WP and PY supplementation during ST on body composition, strength, and gut microbiome in untrained older adults. Seventeen untrained adults (60-70 years) were randomized to either consume WP (25 g) or PY (24.5 g) along with an 8-week supervised ST program (3 sessions/week). Initial and final assessments included body composition (BIA), strength (10RM, isokinetic torque, handgrip), gait speed, resting metabolic rate, and gut microbiome (16 S rRNA sequencing). Data were analyzed using repeated-measures ANOVA and diversity metrics. Both groups increased skeletal muscle mass (WP: +0.47 kg; PY: +0.50 kg) and improved strength and gait speed (p < 0.01), with no between-group differences. Fat mass decreased only in WP (p = 0.02), while resting metabolic rate increased in PY (p = 0.03). Microbiome analysis revealed distinct shifts: WP increased the Firmicutes/Bacteroidota ratio and enriched Subdoligranulum, whereas PY enhanced alpha diversity and increased the abundance of Coprococcus. Functional pathway predictions indicated differential enrichment in metabolic and signaling processes. High-protein yogurt and whey protein similarly improve muscle mass, strength, and functional capacity during ST, while exerting distinct effects on gut microbiome composition. Yogurt represents a cost-effective alternative to whey protein and may confer additional gut health benefits.Trial registration: Clinicaltrials.gov identifier NCT06412302. Date of registration 06/05/2024.