Scientists at APC Microbiome Ireland, part of University College Cork, studied how coffee talks to the brain through the gut. They looked at the gut‑brain connection, a two‑way street between our stomach and our mind.
The study appeared in Nature Communications and was funded by the Institute for Scientific Information on Coffee. It found that drinking coffee—whether it has caffeine or not—can change the microbes in our gut and affect how we feel.
How Coffee Influences Gut Bacteria and Mood
People have known that coffee can help digestion and mood, but the exact reasons were unclear. This research measured many body signs and mental‑health scores to see what coffee really does.
What Happened in the Test
First, regular coffee drinkers stopped their brew for two weeks. During this break, researchers kept collecting stool samples and mood questionnaires. Without coffee, the mix of chemicals made by gut microbes shifted noticeably.
After the break, participants slowly started drinking coffee again. They didn’t know if they received caffeinated or decaf coffee. Half got decaf, the other half got regular coffee. Both groups felt better—less stress, fewer sad thoughts, and calmer impulses. This shows coffee can lift mood even without caffeine.
Bacteria That Like Coffee
The team spotted more of two bacteria in coffee lovers: Eggertella sp. and Cryptobacterium curtum. These bugs help make acids and bile, which protect the gut from bad germs. They also saw more of a group called Firmicutes, which earlier studies linked to happy feelings in women.
Decaf vs. Caffeine Effects
Only the people who drank decaf showed better learning and memory. This hints that other coffee compounds, like polyphenols, may help the brain.
Those who drank caffeine‑filled coffee felt less anxious and stayed more alert. Caffeine also seemed to lower signs of inflammation.
What the Researchers Said
"Our results show how coffee changes gut microbes and brain responses. Over time, coffee could help keep the microbiome healthy," the scientists wrote.
Professor Cryan added, "Coffee is more than just caffeine. It works with our gut bugs, our metabolism, and even our feelings. Both regular and decaf coffee can support health in different ways."