A groundbreaking microbiome study from APC Microbiome Ireland challenges the long-held assumption that caffeine drives coffee’s health effects. The controlled 5-week trial of 62 adults—comparing habitual coffee drinkers to non-drinkers—reveals that decaffeinated and regular coffee produce identical shifts in gut bacterial composition. This finding suggests that coffee’s 98–99% non-caffeine fraction, particularly chlorogenic acids and melanoidins formed during roasting, are the true architects of microbiome remodeling. These polyphenolic compounds, which constitute 7–10% chlorogenic acids and 5–8% melanoidins by weight, appear to drive measurable changes in bacterial populations and metabolite production. While the study is exploratory and limited in sample size, the results underscore the need to shift focus from caffeine-centric research toward understanding how the broader coffee matrix influences gut health. Larger, longer-term replication studies are essential to confirm these preliminary findings and clarify their clinical significance.
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