Researchers studying 62 adults have found that both caffeinated and decaffeinated coffee alter the gut microbiome in ways that appear to reduce stress, lower depression scores, and improve cognitive function, pointing to benefits that go well beyond caffeine.
The study divided participants into two groups: 31 regular coffee drinkers who consumed three to five cups daily, and 31 non-drinkers. Coffee drinkers first abstained for two weeks, a period during which researchers observed notable shifts in gut metabolite profiles. When coffee was reintroduced in a blinded trial, half consumed caffeinated and half decaffeinated versions.
Both groups reported reduced stress, depression, and impulsivity after reintroducing coffee. Researchers also recorded increases in specific gut bacteria associated with digestion and immune function. The split between the two types of coffee revealed distinct effects: decaffeinated coffee was linked to improved learning and memory, while caffeinated coffee was associated with reduced anxiety, sharper attention, and lower markers of inflammation.
Coco Pierrel, a certified integrative nutritionist and founder of Eat Shed Glow, was not involved in the research but told Healthline the findings confirm what gut health specialists have observed clinically. "Coffee feeds your gut microbes through plant compounds called polyphenols and fiber-like molecules called melanoidins," she said. Those compounds are fermented by gut bacteria into short-chain fatty acids, which then send signals to the brain via the vagus nerve.
Caffeine itself works through a separate mechanism, blocking adenosine receptors in the brain to increase alertness while also stimulating gastric activity. But the study's most striking finding may be that decaf coffee produced measurable cognitive and emotional benefits on its own.
"The polyphenols in coffee, whether caffeinated or decaffeinated, lower inflammation, and chronic low-grade inflammation is one of the most underrated drivers of low mood and anxiety," Pierrel said.
The research adds to a growing body of evidence around the gut-brain axis, the two-way communication system connecting the digestive tract and the central nervous system. Coffee, in this framework, functions as more than a stimulant. According to Pierrel, it is "one of the few daily habits that synchronizes your metabolism with your mental clarity."
The study's sample size was small, and further research with larger populations will be needed to confirm the findings. Still, the results suggest that people who drink decaf for health or sensitivity reasons may be capturing more of coffee's benefits than previously understood.
