Irish Microbiome Study Reveals How 3-5 Daily Cups of Coffee Reshape Human Gut-Brain Communication

New Irish research shows how 3-5 cups of coffee daily can alter gut bacteria to reduce stress, improve memory, and support a healthier microbiome.

By: AXL Media

Published: Apr 21, 2026, 9:27 AM EDT

Source: Information for this report was sourced from EurekAlert

The Neurological Impact of Daily Brewing Habits

A comprehensive study published in Nature Communications has identified how coffee serves as a dietary intervention for the microbiota-gut-brain axis. By monitoring participants over periods of abstinence and reintroduction, scientists at University College Cork discovered that drinking 3 to 5 cups of coffee daily initiates a complex series of chemical signals between the gut and the brain. According to Professor John Cryan, the principal investigator at APC Microbiome Ireland, coffee acts as more than a simple stimulant, functioning as a complex dietary factor that interacts directly with human metabolism and emotional stability.

Quantifying the Connection Between Microbes and Mood

The clinical investigation involved 62 participants who were divided into regular coffee consumers and non-drinkers to track physiological and psychological changes. After a mandatory two-week period of total coffee abstinence, which caused visible shifts in gut metabolite profiles, the reintroduction of the beverage led to measurable improvements in mental health metrics. Data from the study suggests that participants experienced lower scores in perceived stress, depression, and impulsivity regardless of whether the coffee they consumed contained caffeine, highlighting the importance of the bean's non-stimulant compounds.

Bacterial Shifts Linked to Improved Digestive Health

The research team observed significant increases in specific bacterial populations, including Eggertella sp and Cryptobacterium curtum, among the coffee-drinking cohort. These microbes are essential for regulating gastric acid secretion and bile acid synthesis, which are critical processes for eliminating harmful stomach infections and maintaining gut balance. Additionally, an increase in Firmicutes bacteria was documented, a biological marker that researchers have previously associated with the presence of positive emotions, particularly in female subjects.