Coffee may influence gut bacteria and how people feel even when it contains little caffeine. In a small Irish study, regular coffee drinkers reported less stress after resuming coffee following a break, whether they were given regular coffee or decaf.
The findings give researchers a way to separate some of the effects of caffeine from those of the many other compounds in coffee. They also raise the question of whether changes in gut microbes and changes in mood are connected.
Researchers at University College Cork and APC Microbiome Ireland reported the work in Nature Communications . They recruited 62 healthy adults aged 30 to 50, split evenly between people who never drank coffee and people who usually had three to five cups a day.
At the start, the team compared the two groups using questionnaires, thinking tasks and samples such as stool and urine. The people who never drank coffee took part in that initial comparison, while regular drinkers continued into the next stage.
Regular drinkers took a two-week break from coffee and other sources of caffeine specified by the study. They were then randomly assigned to receive instant coffee with caffeine or decaf for three weeks, witho...