Both protein yogurt (24.5g) and whey protein isolate (25g) generated identical muscle gains of approximately 0.5kg over 8 weeks of strength training in adults aged 60-70, along with similar improvements in strength and gait speed. However, whey protein uniquely reduced fat mass while yogurt increased resting metabolic rate. The microbiome responses diverged dramatically: whey protein increased the Firmicutes/Bacteroidota ratio and enriched Subdoligranulum bacteria, while yogurt enhanced alpha diversity and boosted beneficial Coprococcus species. This finding challenges the premium pricing and widespread preference for whey protein supplements among older adults seeking to combat sarcopenia. Yogurt's ability to deliver equivalent muscle-building results while potentially improving gut health diversity represents a paradigm shift toward whole food protein sources. The microbiome differences suggest yogurt may offer superior long-term health benefits, given that gut diversity typically declines with aging and correlates with overall health outcomes. However, the small sample size of 17 participants limits generalizability, and longer studies are needed to determine whether these microbiome changes translate into measurable health advantages beyond muscle preservation.