Drinking three to five cups of coffee a day can alter the composition of gut microbiota and help ease stress and depression, contributing to mental health, according to a new analysis. Decaffeinated coffee was linked to improvements in learning and memory, while caffeinated coffee was associated with enhanced focus and attention.
According to the medical community on Tuesday, researchers at APC Microbiome Ireland, affiliated with University College Cork in Ireland, recently published a paper in the international journal Nature Communications that identified the pathway through which coffee acts on the "gut-brain axis." The gut-brain axis refers to a system in which the digestive tract and central nervous system exchange bidirectional signals mediated by microbes and metabolites.
The researchers recruited 31 regular coffee drinkers and 31 non-drinkers for a comparative experiment. Participants underwent psychological evaluations and recorded their diets and caffeine intake, while gut bacteria and emotional changes were measured together through stool and urine samples. The coffee group was limited to those who regularly drink three to five cups a day, a range the European Food Safety Authority (EFSA) considers safe as a daily recommendation.
The experiment first began with the coffee group abstaining from coffee for two weeks. The researchers tracked biological samples and mental health indicators during this period. As a result, noticeable shifts in the metabolite patterns produced by gut microbiota were observed after quitting coffee, and a gap from the non-drinker group was also confirmed.
In the subsequent stage, participants were given coffee again in a way that made it impossible to distinguish whether it contained caffeine. Half drank regular coffee, while the rest drank decaf. Both groups showed improved mood, with lower indicators of stress, depression, and impulsivity. The researchers interpreted this as meaning that coffee without caffeine can also have a positive effect on emotions.
In the gut microbiome analysis, levels of "Eggerthella sp." and "Cryptobacterium curtum" stood out in the coffee-drinking group. These microbes are involved in acid production and bile acid synthesis in the digestive tract and are known to contribute to defending the body against harmful bacteria and infections. The "Firmicutes" family, which has been reported to be closely linked to positive emotions, also increased.
In terms of cognitive function, the effects of the two types of coffee diverged. Improvements in learning ability and memory were detected only in participants who drank decaf. The researchers suggested that components other than caffeine, such as polyphenols, may have boosted some cognitive functions. Those who drank caffeinated coffee experienced reduced anxiety and heightened focus and attention, with a link to lower inflammation risk also noted.
John Cryan, a professor at University College Cork and lead researcher of the study, said, "Interest in gut health has risen sharply recently, and the connection between digestive health and mental health is also gradually being uncovered, but the mechanism by which coffee acts on the gut-brain axis was not clear."
"This study shows how coffee affects gut microbiota and neurological responses, as well as the potential benefits it may have in forming a healthy gut environment over the long term," Cryan stressed. "Coffee can influence the activity of gut microbiota and the way metabolites are utilized." He added, "Coffee is not simply a caffeinated beverage but a complex dietary element that interacts with gut microbes, metabolism, and even emotional health. It suggests that caffeinated and decaffeinated coffee may affect health in different ways."
