Gut bacteria may play a key role in mental health by affecting the way genes are expressed in the brain, scientists have found.

The link between gut bacteria and anxiety has been the focus of much research in recent years, but determining how the microbiome affects your mental health has been a mystery until now, International Business Times reports.

New research by University College Cork found that anxious mice raised in a microbe-free environment express genes in the brain differently due to changes in their microRNA, according to the study in the journal Microbiome.

"This is important because these microRNAs may affect physiological processes that are fundamental to the functioning of the central nervous system and in brain regions, such as the amygdala and prefrontal cortex, which are heavily implicated in anxiety and depression," said study author Gerard Clarke in a statement.

Just how the gut bacteria are regulating the microRNAs is still not clear. More research is needed before clinical trials can be carried out to assess the impact of changing gut bacteria on mental health.

But the new findings suggest that improving your gut health by eating prebiotic foods rich in fiber could well end up being good for your mental health.

"This is early-stage research but the possibility of achieving the desired impact on microRNAs in specific brain regions by targeting the gut microbiota – for example by using psychobiotics – is an appealing prospect," said Clarke.