GUT BACTERIA AND the Brain

Anyone

who has had an anxious knot in their stomach knows that the gut and mood are related. That’s partly due to the vagus nerve, a nerve that runs directly from the gut to the brain. Studies suggest that the brain and gut are in constant dialogue, communicating using the nervous system as well as the blood stream and hormones.

There’s mounting evidence that the composition of bacteria species in the gut is also linked to changes in the brain’s structure and how it functions. Scientists think the metabolites produced by the gut bacteria enter the blood and can cause inflammation, contributing to brain diseases such as Parkinson’s, Alzheimer’s and autism. People with mental illnesses such as depression, anxiety and schizophrenia have all been shown to have dramatically different gut bacteria to those found in a healthy gut.

It appears the gut microbiome can affect behaviour, too. A Canadian study using mice has shown that exposure to antibiotics can affect the brain, causing changes to the blood–brain barrier and other changes in the frontal cortex. The young mice became more aggressive and their social interaction changed compared to mice whose gut bacteria had not been exposed to antibiotics. When they were given probiotics as well as antibiotics, there were fewer changes to their brains and behaviour.

It’s still not clear why the gut affects the brain in this way, but we know that serotonin, the chemical associated with mood, is mostly produced in the gut. It’s also thought that the bacteria’s metabolites can affect the chemistry of the brain, affecting human mood and behaviour.