When you fall in love, you feel butterflies in your stomach; before an important event, you may have a stomachache; stress can prompt a visit to the WC; when you are hungry, you may experience a foul mood, but as soon as you taste your favourite meal, you feel well and pleased. Every day we experience how the brain and the gut are connected and how they “talk” to each other.

This bidirectional communication was discovered decades ago and that is also when the term “second brain” was coined to refer to the gut, as it contains even more neurons than the human spinal cord.

Recent studies in this fascinating field have shown the 100 trillion microorganisms inhabiting our body may rule our mood and even mental health; they appear to be related, for example, to anxiety and depression, and the latest research points out a link between an unbalanced microbiota and brain-related diseases such as Alzheimer’s, Parkinson’s and multiple sclerosis.

“It’s frightening to think that our mood is dependent on our guts, that really this consortia of bacteria are, in a way, controlling our brain,” says Bercik

“It’s frightening to think that our mood is dependent on our guts, that really this consortia of bacteria are, in a way, controlling our brain,” states Premsyl Bercik, from McMaster University, in Canada, one of the pioneering researchers in this field of neurogastroenterology. He studies precisely this connection between our “two brains” and how disruptions of the gut microbiota can modulate behaviour and maybe even brain-related disease.

“Experiments showing this connection between gut and brain are now really a hot topic in gastroenterology and neuropsychiatry science,” says Bercik, who attended the 6th edition of Gut Microbiota for Health World Summit, held in Paris in March, 2017.

The experiments Bercik refers to have demonstrated how brain and gut talk to each other. One of them consisted in introducing pathogenic bacteria to animal model intestines. It has been seen the brain is able to notice the presence of these abnormal bacteria within a few hours, even before an immune response is launched. Bercik also did made experiments showing this communication. In fact, his experiments were one of the first ones to show that when gut microbiota composition is altered, behaviour is affected.

“I think the most striking experiment we did was when we treated mice with a mixture of non-absorbable antibiotics which changed the composition of gut bacteria. We realised there was a significant change in the behaviour of the mice,” he recalls. “In the lab we had mice that were usually shy and did not move very much. But suddenly, after treating them with these antibiotics they suddenly ‘woke up’ and started exploring the environment!”

They also saw that after one or two weeks, when the gut microbiota returned to normal, the behaviour of mice also normalised.

So, if gut microbiota perturbations can affect the brain in animals, can we use the microorganisms in our intestines to influence our own mood and behaviour? According to Bercik, there is some evidence coming from patients who suffer from depression and anxiety: they have different microbiota profiles, in comparison to healthy individuals. And in experiments in which scientists have transplanted the microbiota from these patients into germ-free mice, they have observed that the animals reproduced some of the behavioural traits of the human patients.

“There is definitely a possibility that just by changing the gut microbiota composition or just changing the metabolic activity of the bacteria we have in the gut we could also affect the behaviour in humans, healthy humans or in patients,” says Bercik.

In changing the gut microbiota, probiotics could turn out to be useful. Treatments with specific probiotics could help regulate an unbalanced microbiota and thus improve, for instance, depression symptoms. Bercik and colleagues are, in fact, working on this possibility. “Once we prove these probiotics have a really significant effect on mental health, probably in five or ten years we will be able to have this kind of treatment available to a wide public,” he explains. So, it’s possible that a decade from now you’ll be able to “go to a supermarket and buy a ‘happy’ probiotic—bacteria that will make you feel well”.