Coffee can affect much more than alertness. New research suggests that both regular and decaffeinated coffee can alter the gut microbiome and may influence mood, stress, memory, and attention through the gut-brain connection.
Scientists at APC Microbiome Ireland, a research center at University College Cork, investigated in detail how coffee can influence communication between the digestive system and the brain.
The study published in Nature Communications and sponsored by the Institute for Scientific Information on Coffee (ISIC), found that both caffeinated and decaffeinated coffee were associated with changes in the gut microbiome, as well as differences in mood and stress.
How coffee can affect the gut-brain connection
Scientists have long studied coffee for possible effects on digestion, mood, and overall health, but exactly how these effects arise is less clear.
The new research focused on the microbiota-gut-brain axis, the two-way communication system that links microorganisms in the digestive tract to the brain. Signals can travel between the gut and the brain through immune activity, hormones, nerves, and chemicals produced by microbes.
The researchers examined 31 regular coffee drinkers and 31 people who did not normally drink coffee. Participants completed psychological assessments and kept records of caffeine intake and diet. The researchers also collected stool and urine samples to track changes in gut microbes, metabolism, mood, and perceived stress.
For the study, “coffee drinkers” were considered those who regularly consume 3 to 5 cups of coffee a day, an amount defined by the European Food Safety Authority (EFSA) as a safe and moderate amount for most people.
What happened when coffee was eliminated?
Regular coffee drinkers first stopped consuming coffee for two weeks. During that period, participants repeatedly completed psychological assessments and provided stool and urine samples.
When coffee drinkers stopped drinking coffee, researchers observed substantial changes in their gut metabolite profiles compared to people who did not normally consume coffee. Metabolites are small molecules produced or altered during metabolism, including compounds created by gut microbes when they 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 returned to their diets, both groups reported lower scores of perceived stress, depression, and impulsivity. The findings suggest that some of coffee’s effects on mood may not depend entirely on caffeine.
Coffee linked to changes in gut bacteria
The researchers also found differences in several types of gut bacteria.
Bacteria, like ‘Eggertella sp.‘ either ‘cryptobacteria curtum‘, were more abundant among coffee drinkers than among non-coffee drinkers. ‘Eggertella sp.‘ is believed to contribute to the secretion of acid in the stomach and intestines, while ‘cryptobacteria curtum‘ may participate in the production of bile acids.
Both processes could help create an intestinal environment that will discourage certain harmful bacteria and infections.
The researchers also observed higher levels of Firmicutes bacteria, a broad group of microbes that has previously been associated with positive emotions in women.
Decaffeinated coffee and caffeinated coffee showed different effects
One of the most intriguing findings was that caffeinated and decaffeinated coffee did not seem to affect participants in exactly the same way.
Improvements in learning and memory were only seen among participants who drank decaffeinated coffee. That finding suggests that substances other than caffeine may contribute to some of coffee’s effects on cognition.
Coffee contains thousands of chemical compounds, including polyphenols. These plant-derived substances can act as antioxidants and can also interact with gut microbes, potentially influencing metabolism and other biological processes.
Meanwhile, caffeinated coffee was associated with reduced feelings of anxiety, as well as improved alertness and attention. Caffeine was also linked to a reduced risk of inflammation.
Because the study involved a relatively small number of participants, the findings do not establish that coffee directly causes these changes in mood, cognition, or gut health. However, they provide new clues about biological pathways that could help explain associations reported in previous coffee research.
Coffee is more than caffeine
Corresponding author of the study, Professor John Cryan, Principal Investigator at APC Microbiome Ireland, University College Cork, commented: “Public interest in gut health has increased enormously. The relationship between digestive and mental health is also becoming better understood, but the mechanisms behind coffee’s effects on this gut-brain axis remain unclear.
“Our findings reveal the microbiome and neurological responses to coffee, as well as its potential long-term benefits for a healthier microbiome. Coffee can modify what microbes do together and what metabolites they use. As the public continues to consider dietary changes to achieve proper digestive balance, coffee also has the potential to be leveraged as an additional intervention as part of a healthy, balanced diet.”
The findings add to growing evidence that coffee should not be viewed simply as a source of caffeine. Its many other components can interact with the microbiome, metabolism and nervous system in different ways.
“Coffee is more than caffeine – it is a complex dietary factor that interacts with our gut microbes, our metabolism and even our emotional well-being,” Professor Cryan said. “Our findings suggest that coffee, whether caffeinated or decaffeinated, may influence health in different but complementary ways.”