Caffeine comprises merely 1–2% of coffee’s chemical composition, yet for decades has dominated discussion of the beverage’s health impacts. New microbiome data reveal a starkly different picture: chlorogenic acids account for 7–10% of coffee by weight, while roasting-derived melanoidins contribute 5–8%—compounds with far greater biological relevance to human health than caffeine itself. In a controlled intervention trial, both regular and decaffeinated coffee induced identical shifts in gut bacterial populations, providing direct evidence that polyphenols drive microbiome remodeling rather than caffeine. These polyphenolic compounds trigger measurable changes in bacterial metabolite production, including shifts in indole and short-chain fatty acid pathways. The findings fundamentally reframe how researchers and clinicians should conceptualize coffee’s pharmacological profile, shifting emphasis from a single alkaloid to a complex matrix of bioactive plant compounds. Understanding coffee’s true active constituents opens new avenues for optimizing beverage consumption and developing targeted microbiome interventions.
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