Friendly bacteria can act as a stress buster and improve mental health, research has shown.
A study of 22 healthy men found that volunteers who took a probiotic for a month experienced less daily stress than those given a "dummy" placebo supplement.
Tests also showed they performed better in a visual memory task.
Previously the same team found that the bacterial strain Bifidobacterium longum 1714 reduced stress, anxiety and depressive symptoms and improved memory in mice.
Lead researcher Dr Andrew Allen, from the APC Microbiome Institute at University College Cork, Republic of Ireland, said: "These findings could be taken forward into people with psychological disorders related to stress, such as generalised anxiety disorder or major depression."
The research was presented at the Society of Neuroscience annual meeting in Chicago.
At the start of the study and again after four weeks the scientists measured participants' acute stress, memory and brain activity.
Self-reported perceived stress and measured physical responses to stress were reduced in volunteers given the probiotic containing B. longum 1714.
The findings suggest that the bug may prove useful for alleviating stress-related conditions, though further studies involving more participants were needed, said the researchers.