How might gut health affect mental health and wellbeing?
By Dr Sonja Kukuljan and Dr Tim Crowe
Many would agree that one key thing separating us from other animals is our minds. Well, emerging evidence suggests that our human gut bacteria may well be playing a hand in the way we think and feel, or in other words our mental wellbeing. This two-way communication link between our gut and central nervous system is called the gut-brain axis.
The idea that gut bacteria may affect our mood and mental wellbeing essentially started with an early study in rodents, which found that germ-free mice (i.e. those without gut bugs) produced around twice the stress hormones compared with mice which had gut bugs. So, those with good gut bug colonies had less stress. By the way, a good or healthy gut bacteria colony is one that has a diverse mix of gut bacteria.
More research followed, so that now there is large body of animal research linking germ-free status with behavioral changes, including anxiety.
Other studies then found that when gut bacteria from humans with depression were transplanted to rodents, then markers of depressed behavior (yes, there are some!) become prevalent in the transplanted rodents. Experts in the area now suggest there may be a link between reduced gut bacteria ‘diversity’ in patients with depression, relative to a ‘healthy’ person, so that it is possible that poor gut bacterial diversity is at least partly involved in the development of depression.
The gut microbiota plays an important part in the gut-brain connection from its influence on the host by endocrine, neural, and immune pathways and in this way, potentially affect brain function, cognition and behavior. That’s a start to the possible link between gut bugs and mental wellbeing. Other mechanistic ways by which gut bugs may be interacting with our state of mind include via the vagus nerve, or the key nerve that connects sensation communication between the gut and the brain. Other possibilities include that the gut bacteria affect the immune system, around 70% of which resides in the gut: here, improved immunity could impact on our sense of overall wellbeing. Still other possible mechanisms link uptake by the body of by-products of ‘healthy’ gut bacteria fermentation, especially short chain fatty acids like butyrate, to improved mental wellbeing.
It’s important to end this short discussion by saying it is way too soon to understand all the implications of research in this area. We need large scale, human studies that are capable of identifying the gut bacteria groups, species, sub-species (yes, you get the pictureJ) that may be involved in these gut-brain axis interactions before we really understand the full picture, but the early signs are extremely positive.