Not just the caffeine. A new study reported by ScienceDaily suggests coffee may affect the brain through the gut. Researchers at APC Microbiome Ireland and University College Cork discovered that both caffeinated and decaffeinated coffee were associated with alterations in gut microbes and metabolites linked to mood, stress and cognitive function. Those who resumed coffee drinking after a two-week break reported lower levels of perceived stress, depression and impulsivity. The findings, published in Nature Communications, also showed differences between regular and decaffeinated coffee, with decaf associated with better learning and memory, and caffeinated coffee with less anxiety and better attention. However, the study was small and does not prove that coffee directly improves mental health.
Looking beyond caffeine
Coffee is often viewed as a quick way to feel more awake, particularly at the start of a demanding day. Its effects, however, may extend well beyond alertness. Coffee contains caffeine, but it also includes polyphenols, phenolic acids and other plant compounds that can interact with the body’s metabolism and the microorganisms living in the digestive system.The study explored the microbiota-gut-brain axis, the two-way communication network connecting the gut and the brain. Signals can travel between these systems through the immune system, hormones, nerves and chemicals produced when gut microbes process food and drinks. That suggests changes in the gut microbiome could affect mood, stress responses and parts of cognition, although scientists are still working out how exactly it does so.To study this connection, researchers studied 31 habitual coffee drinkers and 31 people who didn’t regularly drink coffee. Three to five cups a day was the usual intake for regular coffee drinkers. They first stopped drinking coffee for two weeks, allowing researchers to observe what changed when coffee was removed from their routines. Coffee was then added back for 21 days, with participants receiving either caffeinated or decaffeinated coffee without knowing which type they were drinking, as per the report.
Mood changes after coffee returned
When coffee was reintroduced, both groups reported lower scores for perceived stress, depression and impulsivity. This was one of the most significant findings because it suggests that some of coffee’s possible effects on mood may not depend entirely on caffeine. If caffeine were responsible for every change, researchers would not necessarily expect decaffeinated coffee to show similar associations.The findings also suggested that regular and decaffeinated coffee may have different effects on people. Those who drank caffeinated coffee reported feeling less anxious and less psychologically distressed. Caffeinated coffee has also been linked to greater vigilance and attention. Decaffeinated coffee, meanwhile, was linked to improvements in learning and episodic memory, as well as better sleep quality and increased physical activity.These findings should be taken with caution. The study involved a small number of people and the participants were healthy adults. Also, some memory improvements could have been affected by better sleep, more physical activity or familiarity with the tests. The researchers also relied partly on questionnaires, which measure how participants felt and behaved but cannot capture every aspect of mental health.
Gut bacteria react to coffee
The researchers found that coffee drinking was associated with changes in some gut bacteria, including Eggertella species and Cryptobacterium curtum. They also noticed changes in members of the Firmicutes group.” These changes were not just a general increase in microbial diversity. Instead, coffee appeared to influence particular strains within the gut community.The study also identified changes in metabolites, which are small molecules made or changed in the course of metabolism. Some of the compounds seemed to be coming directly from coffee itself, while others were linked to the activity of gut microbes. Caffeine-related chemicals appeared in the caffeinated coffee group, but several coffee-related phenolic compounds changed after both caffeinated and decaffeinated coffee were consumed.This may help explain why decaf appeared to have effects of its own. Coffee’s non-caffeine compounds can be processed by gut bacteria, and the resulting metabolites may influence biological pathways involved in inflammation, mood and brain function. The researchers found statistical links between certain microbial species, metabolites and cognitive or behavioural measures, but these links do not yet establish a direct cause.
What the study does not prove
The findings do not mean that coffee can prevent depression, treat anxiety or replace professional mental health care. They also do not suggest that everyone should begin drinking several cups of coffee each day. A person’s response to coffee can depend on genetics, sleep, diet, medication, caffeine sensitivity and existing medical conditions.Too much caffeine may cause restlessness, digestive discomfort, a racing heartbeat or difficulty sleeping. For some people, especially those who are sensitive to caffeine, these effects may outweigh any possible benefits. Decaffeinated coffee may be a suitable alternative for people who enjoy the flavour and routine of coffee but want to reduce caffeine intake, although it is not automatically appropriate for every individual.The study was sponsored by the Institute for Scientific Information on Coffee, and its authors acknowledge that the sample size was limited. Larger and longer studies will be needed to determine whether the changes observed in the gut actually lead to improvements in mood or cognition, or whether coffee drinking is simply associated with other healthy habits.
A more complex picture of coffee
The research adds to evidence that coffee is more than a source of caffeine. Its compounds may interact with gut microbes, metabolism, the immune system and the nervous system in ways that differ between individuals. The results also show why researchers are increasingly examining ordinary foods and drinks through the lens of the gut-brain connection.For people who already like coffee, the study offers an interesting explanation as to why the beverage may affect energy, stress and concentration in different ways. The safest takeaway is not to treat coffee as a cure-all, but as one part of a balanced lifestyle that includes adequate sleep, nutritious food, movement and appropriate mental health support.
