How coffee affects the gut-brain connection

Scientists at APC Microbiome Ireland, a research center at University College Cork, investigated how coffee may affect communication between the digestive system and the brain.

Research published in Nature Communications found that both caffeinated and decaffeinated coffee were associated with changes in the gut microbiome, as well as differences in mood and stress. The study was sponsored by the Institute for Coffee Science and Information Research (ISIC).

The research focused on the microbiota-gut-brain axis, a two-way communication system linking microorganisms in the gastrointestinal tract with the brain. Signals can travel between the gut and brain through immune activity, hormones, nerves and compounds produced by microbes.

Researchers surveyed 31 regular coffee drinkers and 31 people who did not drink coffee. Participants completed psychological assessments and recorded their caffeine intake and diet. The researchers also collected stool and urine samples to examine gut bacteria, metabolism, mood and perceived stress.

The study defined a coffee drinker as someone who regularly consumed three to five cups of coffee per day. The European Food Safety Authority (EFSA) considers this a safe and moderate amount for most people.

What happened when participants stopped drinking coffee?

Regular coffee drinkers stopped consuming coffee for two weeks. During this period, they repeatedly completed psychological assessments and provided stool and urine samples.

After coffee was removed from their diets, researchers observed significant changes in the participants’ gut metabolite profiles compared with those of people who did not regularly drink coffee. Metabolites are small molecules produced or altered during metabolism, including compounds created when gut microorganisms process food and other substances.

Coffee was then reintroduced without participants knowing whether they were drinking caffeinated or decaffeinated coffee. Half received decaffeinated coffee, while the other half received caffeinated coffee.

After coffee was reintroduced, both groups reported lower scores for perceived stress, depression and impulsivity. The results suggest that some of coffee’s effects on mood may not depend entirely on caffeine.

Coffee was linked to changes in gut bacteria

The researchers also identified differences in several types of gut bacteria.

Bacteria such as Eggerthella species and Cryptobacterium cultum were more common among coffee drinkers than non-coffee drinkers. The genus Eggerthella is thought to contribute to acid secretion in the stomach and intestines, while Cryptobacterium cultum may be involved in bile acid production.

These processes may help create a gut environment that protects against certain harmful bacteria and infections.

The researchers also observed higher levels of bacteria from the Firmicutes group, a broad category of microorganisms previously associated with positive emotions in women.

Did decaf and caffeinated coffee affect the body differently?

One of the study’s most notable findings was that caffeinated and decaffeinated coffee did not appear to have exactly the same effects.

Improvements in learning and memory were observed only among participants who drank decaffeinated coffee. This finding suggests that compounds other than caffeine may contribute to some of coffee’s effects on cognition.

Coffee contains thousands of compounds, including polyphenols. These plant-derived substances can act as antioxidants and interact with gut bacteria, potentially influencing metabolism and other biological processes.

Caffeinated coffee, meanwhile, was associated with reduced anxiety and increased vigilance and alertness. Caffeine was also associated with a lower risk of inflammation.

What the findings mean for coffee and gut health

Because the study included a relatively small number of participants, the results do not establish that coffee directly causes changes in mood, cognition or gut health. However, they offer new clues about biological pathways that may help explain associations reported in earlier coffee research.

Professor John Cryan, the study’s corresponding author and principal investigator at APC Microbiome Ireland at University College Cork, said: “There is a huge public interest in gut health. The relationship between the digestive system and mental health is also becoming increasingly understood, but the mechanisms behind coffee’s effects on this gut-brain axis remain unclear.”

“Our findings reveal microbiome and neurological responses to coffee, as well as potential long-term benefits for a healthier microbiome. Coffee can change what microbes do collectively and the metabolites they use. As the public continues to think about dietary changes for proper digestive balance, coffee could also be leveraged as a further intervention as part of a healthy balanced diet.”

The findings add to evidence that coffee should not be viewed solely as a source of caffeine. Its other components may interact with the microbiome, metabolism and nervous system in different ways.

“Coffee is more than just caffeine. It’s a complex dietary element that interacts with your gut microbiome, metabolism and even your mental well-being,” Professor Cryan said. “Our findings suggest that coffee, whether caffeinated or decaffeinated, may affect health in different, but complementary ways.”