Impact of Yogurt and Rolled Oats Consumption on the Gut Microbiome: A Randomized Crossover Study Displaying Individual Responses and General Resilience

BACKGROUND: Yogurt and rolled oats are commonly linked to gut health through probiotic and prebiotic effects, but these potential benefits remain insufficiently studied, especially in healthy individuals. OBJECTIVES: This study primarily aimed to investigate the effects of daily yogurt and rolled oats consumption on gut microbial composition. Secondary outcomes included stool metabolites and blood-based health markers. METHODS: In this randomized, open-label, 2-period crossover trial, 119 healthy participants were randomly assigned to 1 of 2 sequences: 250 g of yogurt daily followed by 250 g of yogurt with 50 g of rolled oats, or the reverse with a washout period in between. Stool and blood samples were collected at baseline and post intervention. Metagenomic sequencing and metabolomic analyses were conducted on stool samples, whereas health markers related to metabolic control, inflammation, immune response, oxidative stress, and gut permeability were assessed in the participants' blood. RESULTS: Of the 119 randomly divided participants, 110 completed the study (53 yogurt first, 57 yogurt and rolled oat first). Yogurt consumption transiently increased yogurt-associated bacteria, with Streptococcus thermophilus rising from absent to 0.97% [95% confidence interval (CI): 0.71, 1.26] in the yogurt intervention and 0.79% (95% CI: 0.58, 1.03) in the yogurt with oats intervention. In a small Prevotella-predominant subgroup (n = 8), adding rolled oats increased microbial evenness (q < 0.001) and reduced interindividual divergence (q < 0.05), suggesting a temporary slight homogenization. No additional effects on fecal short-chain fatty acids concentrations or human health markers were identified. Functional metagenomic changes were mainly driven by yogurt-derived bacterial enrichment. CONCLUSIONS: A healthy gut microbiota is largely stable and resilient to short-term diet changes, yet individual differences highlight the importance of personalized dietary recommendations. CLINICAL TRIAL REGISTRATION NO: (German Trial Register): DRKS00023146 (https://drks.de/search/en/trial/DRKS00023146/details).