Commonly referred to as a ‘second brain’, the role of the gut extends beyond being a digestor of food and drink. In fact, research has demonstrated time and time again the profound partnership between the gut and the brain, and the range of actions elicited by the chemical factory that is our gut microbiome. The gut-brain-axis operates through several pathways and chemical signals that have an influence over our mood, stress levels and cognitive function. So, with the support of the 100 trillion microbes that live within the human digestive system, Australian researchers are discovering how we can improve mental health conditions through diet.
There are several ways in which the gut microbiome is thought to influence mental health. Through constant bidirectional communication, microbes communicate with the nervous system directly and produce a host of neuroactive and anti inflammatory metabolites that can influence pathways important for brain and mental health, says Associate Professor Heidi Staudacher.
Associate Professor Staudacher is an Advanced Accredited Practising Dietitian and mid-career researcher leading Monash University’s Diet, Gut and Brain Group. Following an undergraduate degree in sports science, Associate Professor Staudacher undertook an honours year in nutrition that exposed her to clinical research with a multidisciplinary team and the importance of precision and quality in the research environment.
“My honours year truly sparked my interest in research, but it wasn’t until nearly 10 years later that I came back to research as a fully-fledged dietitian.” said Associate Professor Staudacher.
A dietitian is a professional who applies the science of food and nutrition to promote health, prevent and treat disease to optimise the health of individuals, groups, communities and populations [1].
Dietitians work across many aspects related to the profession, including research, as they endeavor to investigate the links between nutrition and human health and how we can promote good health and prevent disease.
Associate Professor Staudacher and her team are now advancing knowledge of diet-induced microbiome shifts and other mechanisms through which diet influences the brain and the gut. This research is strengthening contemporary management of common mental disorders, such as depression, and disorders of gut brain interaction, such as irritable bowel syndrome (IBS).
A common gastrointestinal disorder, IBS affects 1 in 7 people worldwide. It is characterised by abdominal pain and abnormal bowel habits including diarrhea, constipation or a combination of both. There is currently no known cure for IBS, however, there are many treatments available to support symptom relief.
In the past decade the clinical management of IBS has changed dramatically, and diet is now established as a major treatment method for managing IBS symptoms– a significant discovery as drugs have largely been suboptimal for helping individuals with symptom control.
“In my PhD I was lucky enough to have a wonderful team and together, we showed for the first time that a diet low in fermentable carbohydrates (low FODMAP diet[2]) was better than a placebo diet for people with IBS when delivered through dietary counselling from a dietitian.” said Associate Professor Staudacher.
Study results showed that over 70% of individuals had a clinical response to the low FODMAP group at 4 weeks but that the low FODMAP diet resulted in a drop in Bifidobacteria [3] found in the stool. Most importantly, she and her team showed for the first time that this potentially detrimental shift in the microbiome could be prevented with the addition of a probiotic delivered in conjunction with low FODMAP dietary counselling.
“My research has made a major contribution to the shifting paradigm of medical management towards a more integrated approach to care of people with IBS. Our work underpins clinical guidelines globally, including the recommendations to limit the duration of the low FODMAP diet and to encourage liberalisation of diet in the longer term.” said Associate Professor Staudacher.
Where do mental health and the gut brain axis come into play? Gut disorders, such as IBS, and mental health symptoms commonly occur in the same people. IBS symptoms can precede or come after the development of mental health symptoms. Interestingly, there is also some evidence to suggest that there are shared genetic risk factors for these conditions, indicating that there are some biological processes responsible for both and it isn’t just that one condition causes the other.
Associate Professor Staudacher explains that it makes a lot of sense that in some people IBS could lead to poor mental health. For many, having a chronic gut condition has a huge impact on the way they eat, socialise and work and this undoubtedly will have a toll on mental health over time.
“On the other hand, in a proportion of people, mental health symptoms occur first and then gut symptoms develop later and there seems to be a clear brain-gut link at play here.” Said Associate Professor Staudacher.
There is also data to show that in both IBS and depression, subsets of people have a different microbial profile to people without these conditions. This together with evidence of clinical benefits of microbiome-targeted treatments (e.g. probiotics) in people that have both conditions, suggests microbiome abnormalities in IBS and depression may overlap or are similar in some way.
There has been an explosion in the number of research studies investigating microbiome-targeted dietary interventions for people with depression and several trials have showed it can lead to symptom improvements. However, to now, researchers have not been able to effectively tease out how much of this improvement is due to actual changes in the foods consumed, or to contextual effects like motivational counselling provided by the dietitian or researcher.
Associate Professor Staudacher and her team are now running a first ever double-blind placebo-controlled trial in people with major depressive disorder and providing all their food for 4 weeks whilst monitoring their depressive symptoms.
“This research will help us understand if specific dietary patterns can influence people’s mood alone, without the impact of dietary counselling.” said Associate Professor Staudacher.
Giving us the evidence backing to trust our guts once again.
Diet, Gut and Brain Group research currently recruiting participants:
- OPTIMISM - investigating diet patterns for depression
- Body and Brain – investigating fibre for irritable bowel syndrome
[1] Dietitians Australia, Dietitians and nutritionists, Dietitians and nutritionists | Dietitians Australia.
[2] FODMAPs are a collection of short-chain carbohydrates (sugars) that aren’t absorbed properly in the gut, which can trigger symptoms in people with IBS. A FODMAP diet is intended is for people with medically diagnosed IBS to help manage symptoms.
[3] Bifidobacteria are a healthy bacteria that support the digestion of dietary fiber, prevent infections and produce compounds such as vitamins and other important chemicals.