Coffee May Alter Gut Microbiome to Reduce Stress (Yes, Even Decaf)

Decaf coffee was associated with improved learning and memory, while caffeinated coffee enhanced attention and reduced anxiety and inflammation. Experts say coffee’s polyphenols and other compounds may support mental well-being by lowering inflammation and strengthening communication between the gut and brain. Your morning cup of coffee may be more than just an energizing ritual. New research from APC Microbiome Ireland suggests that both caffeinated and decaffeinated coffee can improve mood and reduce stress by acting on the gut–brain axis. Researchers analyzed 62 adults, including 31 regular coffee drinkers and 31 non-drinkers, using psychological assessments, diet tracking, and stool and urine samples to examine changes in the gut microbiome and mood. Coffee drinkers, defined as those consuming 3 to 5 cups daily, first abstained for two weeks, which led to notable shifts in gut metabolite profiles. When coffee was reintroduced in a blinded trial, half consumed caffeinated and half decaffeinated. Both groups reported reduced stress, depression, and impulsivity, suggesting benefits beyond caffeine. Researchers also observed increases in specific gut bacteria linked to digestion and immune function. Decaffeinated coffee was associated with improved learning and memory, while caffeinated coffee was linked to reduced anxiety, better attention, and lower inflammation, highlighting distinct but complementary effects. How coffee affects the gut-brain axis Coco Pierrel, is a certified integrative nutritionist and founder of Eat Shed Glow, who was not involved in the research. She told Healthline that this study is the first to confirm what gut health specialists have seen in clinical practice for years: that coffee is a functional beverage. “Coffee feeds your gut microbes through plant compounds called polyphenols and fiber-like molecules called melanoidins,” Pierrel explained. “Your gut bacteria ferment these into short-chain fatty acids, which send signals directly to the brain through the vagus nerve.” Pierrel recommended thinking of your gut as a second brain that is in constant communication with your first brain, and coffee is one of the loudest messages you send it every morning. “Caffeine blocks adenosine receptors in the brain to sharpen alertness, while stimulating gastric acid and motility in the gut,” she explained. “Coffee is one of the few daily habits that synchronizes your metabolism with your mental clarity, which is exactly what makes it such a powerful player on the gut-brain axis.” Caffeinated and decaffeinated coffee have health benefits People often associate the mental benefits of coffee with caffeine. However, this study shows that when it comes to lowering stress, boosting learning, and improving memory, decaf coffee has merit too. “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 pointed out. “Those same polyphenols get fermented by gut bacteria into short-chain fatty acids like butyrate, which strengthens the gut barrier and quiets inflammatory signaling to the brain.” Coffee polyphenols also help regulate the HPA axis, the body’s central stress response system, which is likely why both caffeinated and decaf drinkers in this study reported feeling less stressed. “A healthy brain is often the byproduct of a healthy gut,” Pierrel said. Caffeine can boost mental health Still, the study noted some differences between caffeinated and decaffeinated coffee. Caffeinated coffee, in particular, was associated with reduced anxiety and improved vigilance and attention. Why is this the case? “Caffeine blocks adenosine, the molecule that tells your brain it is tired, which is why you feel sharper within 30 minutes of your first cup,” Pierrel explained. “What most people miss is that habitual coffee drinkers develop a blunted cortisol response over time, meaning daily coffee may actually train your nervous system to handle pressure with less reactivity,” she noted. The study also found caffeine specifically reduced inflammation. “When you lower the noise of inflammation in the brain, you naturally raise the signal of focus and vigilance. That is why moderate daily coffee tends to leave habitual drinkers composed rather than just jittery,” Pierrel pointed out. Ways to optimize your coffee intake Of course, you can have too much of a good thing, and how you take your coffee matters, too. “Two to three cups a day is the sweet spot for gut and brain benefits, while more can disrupt sleep and undo the very benefits you are drinking it for,” Pierrel warned. “Sensitivity varies widely based on genetics and metabolism, so some people do best with one cup while others handle three comfortably. I generally recommend a caffeine curfew by 2 pm to protect sleep quality, too.” The real problem is rarely the coffee itself; it is what most people pour into it. Pierrel warned against routinely using flavored syrups, artificial sweeteners, and conventional creamers and milks loaded with seed oils and gut-disrupting gums or additives like carrageenan. “These can compromise the gut lining and cancel the anti-inflammatory benefits the study just demonstrated,” she noted. “The simplest path is black coffee, ideally organic to avoid pesticides and mold. If you take milk, go for grass-fed whole milk or an unsweetened plant milk with a short ingredient list, like Malk or Elmhurst,” Pierrel advised. And if you like sweetness? “Reach for unprocessed maple syrup, raw honey, or zero-calorie natural options like pure stevia or monk fruit extract,” she recommended.