Researchers at APC Microbiome Ireland, based at University College Cork, have made an important discovery about how coffee affects the body. For the first time, they closely studied how coffee, whether or not it contains caffeine, interacts with the 'gut-brain axis,' the system that connects the digestive system and the brain.
The study, published in Nature Communications and supported by the Institute for Scientific Information on Coffee (ISIC), compared 31 regular coffee drinkers with 31 people who don't drink coffee. The participants answered questions about their mental health, recorded what they ate and drank, and gave stool and urine samples. Coffee drinkers in the study usually had 3 to 5 cups a day, which is considered a moderate and safe amount.
At the beginning of the study, coffee drinkers stopped drinking coffee for two weeks. During this time, scientists noticed clear changes in the chemicals produced by their gut bacteria. Their gut activity started to look different from that of non-coffee drinkers.
After the break, coffee was slowly added back, but participants didn't know if they were drinking regular or decaffeinated coffee. Some received decaf, while others had normal coffee. Both groups reported feeling better, with less stress, depression, and impulsive behavior, suggesting that coffee can improve mood even without caffeine.
The researchers also found certain types of bacteria were more common in coffee drinkers. These bacteria may help with digestion and protect against harmful microbes. Another group of bacteria linked to positive emotions, especially in women, was also found in higher amounts.
Interestingly, only people who drank decaffeinated coffee showed improvements in learning and memory. This suggests that other substances in coffee, like plant compounds called polyphenols, might be responsible for these benefits.
"Coffee is more than just caffeine -- it's a complex dietary factor that interacts with our gut microbes, our metabolism, and even our emotional well-being," said corresponding author Professor John Cryan. "Our findings suggest that coffee, whether caffeinated or decaffeinated, can influence health in distinct but complementary ways."
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