Strange as it seems, it’s something we’ve all experienced when we say we have ‘butterflies in the stomach’ when we’re feeling nervous, say researchers who are beginning to see a direct cause-and-effect relationship between the health of our gut and our mental states.

In one experiment with laboratory rats, researchers noticed that the animals’ gut micro-organisms reduced as they were exposed to stressful experiences. Towards the end of the seven-week experiment, the rats seemed to lose any feelings of pleasure and displayed ‘despair-like’ behaviour.

Another group of rats started to display the same behaviour when the micro-organisms from the first set were placed in their gut, suggesting some cause-and-effect pattern.

Other researchers have noted that similar reductions in the gut microbiome have been seen in people suffering from depression and bipolar disorder.