The bacteria that live in our gut are as numerous as the cells in our body. As medical research progresses, the influence that these billions of tiny creatures have on our health is becoming ever more apparent.

It comes as no surprise that they might play a role in gastrointestinal issues, but the microbiome’s influence flies much further afield.Most recently, it has become apparent that there is a significant relationship between gut bacteria and mental health issues, such as depression and anxiety.

Stress, the gut, and the brain

Although the thought of a microorganism in our intestines affecting our mental well-being seems like a leap, the gut and brain are deeply entwined. As an example, most people will know how a nerve-wracking situation can influence the speed of our bowels and, vice versa, how being hungry can cast a shadow over our mood.

A troubled brain can inform the gut, and a troubled gut can inform the brain.

Stress, although it is a mental state, can physically affect our gastrointestinal system and the bacterial residents within it. A recent study found that high levels of stress can affect gut bacteria to a similar degree as a high-fat diet; while other studies have shown that reducing the number of bacteria in the gut can produce stress-induced activity in mice.

So, it seems that the road runs both ways: stress can alter gut bacteria, and gut bacteria can influence stress levels. It is a complicated web.