Are you a fan of coffee but not sure if it's good for you? Perhaps you're aware of its well-known stimulant effect but aren't sure about the other effects it has on your health. A recent study explores how regular coffee consumption influences the gut-brain axis, a bidirectional communication network that connects the digestive system with brain activity. The results reveal a highly complex interaction that goes beyond caffeine.

“Public interest in gut health has risen hugely,” said John Cryan, coauthor of the study published this week in Nature Communications. “The relationship between digestive and mental health is also increasingly being better understood, but the mechanisms behind coffee’s effects on this gut-brain axis have remained unclear.”

Scientists at APC Microbiome Ireland, a research center at the University of Cork, compared 31 healthy adults who regularly consume coffee with 31 non-coffee drinkers. According to the European Food Safety Authority, a “regular” coffee drinker is one who drinks between three and five cups a day, a safe and moderate intake for most people.

The researchers also analyzed what happened when consumers suspended their intake for two weeks and then resumed it, either with caffeinated or decaffeinated coffee. This design made it possible to distinguish the effects of caffeine from the other compounds present in coffee.

“Coffee is more than just caffeine,” said Cryan in a press release, “it’s a complex dietary factor that interacts with our gut microbes, our metabolism, and even our emotional well-being. Our findings suggest that coffee, whether caffeinated or decaffeinated, can influence health in distinct but complementary ways.”

The Surprising Effects of Coffee

One of the most relevant findings was that coffee consumption modifies the composition of the intestinal microbiome. In regular drinkers, changes were detected in the abundance of certain bacteria, such as Eggerthella species and Cryptobacterium curtum, suggesting that coffee favors specific microorganisms. The former are believed to contribute to gastric and intestinal acid secretion, while the latter are involved in bile acid synthesis. APC Microbiome Ireland explains that both bacteria contribute to the elimination of harmful intestinal bacteria, preventing infections.

On the behavioral level, the study found that regular coffee drinkers showed higher levels of impulsiveness and emotional reactivity compared to those who don't partake. However, when coffee intake was suspended for two weeks, these traits decreased, along with some symptoms associated with regular consumption such as fatigue or headache in the first days of abstinence.

The reintroduction of coffee produced different effects depending on the type. Both caffeinated and decaffeinated coffee reduced perceived stress and certain indicators of depression. However, caffeinated coffee was associated with improvements in anxiety and some aspects of attention, while decaffeinated coffee showed benefits in memory, sleep quality, and physical activity. This indicates that many effects of coffee do not depend exclusively on caffeine but on other bioactive compounds, such as polyphenols.

Another relevant aspect was the response of the immune system. Coffee consumers presented lower levels of inflammatory markers and higher levels of anti-inflammatory molecules. During the period of abstinence, some markers of inflammation increased, suggesting that coffee may have a protective effect in this area.

No considerable differences were observed between consumers and non-consumers when it came to physiological stress, as measured by the hormone cortisol. This suggests that, at least under normal conditions, coffee does not substantially alter the body's response to stress, although it may influence the subjective perception of stress, as mentioned above.

A particularly interesting finding of the study was that some effects of coffee on the microbiome and metabolism occur independently of caffeine. Even decaffeinated coffee was able to induce rapid changes in microbial composition after reintroduction. This reinforces the idea that coffee is a complex mixture of compounds with multiple biological effects.

“Our findings reveal the microbiome and nervous system responses to coffee, as well as its potential long-term benefits for a healthier microbiome,” concluded Cryan, who is a principal investigator at APC Microbiome Ireland. “Coffee could modify the activity of microbes as a whole and the metabolites they use. As the population continues to reflect on dietary changes for proper digestive balance, coffee can also be used as an additional intervention within a healthy, balanced diet.”

This story originally appeared on WIRED en Español and has been translated from Spanish.