Effects of whey protein isolate on the human gut microbiota and intestinal function in older adults

Whey protein is commonly used to prevent sarcopenia in older adults due to its high digestibility and amino acid content. Its bioactive components may also influence the gut microbiota, which plays a growing role in healthy aging as microbial composition shifts with age. This study investigated whether daily supplementation with whey protein isolate (WPI) improves gut microbiota diversity and composition in older adults. Sixteen participants consumed 59 g of WPI (35 g of protein) daily for 3 wk. Whey protein isolate significantly increased Simpson diversity in individuals with low baseline diversity, with effects appearing by d 3 and persisting after intervention. Taxonomic analysis revealed increases in beneficial taxa (e.g., Ruminococcaceae, Faecalibacterium, and Christensenella) and reductions in potentially harmful groups (e.g., Proteobacteria, Streptococcaceae, and Colidextribacter), particularly in the low diversity group. Analysis of compositions of microbiomes with bias correction based on absolute abundance confirmed increases in probiotic genera including Lactobacillus, Lactococcus, and Christensenella. Despite these microbial shifts, no significant changes were observed in gastrointestinal symptoms or stool consistency. These findings highlight the potential of WPI supplementation as a dietary strategy to promote a healthier gut microbiome in older adults, particularly in those with low baseline diversity.