Microbiome & psychobiotics, a scientist’s opinion
Interview with Dr. Jason A. Martin, Senior Postdoctoral Fellow at APC Microbiome Ireland, University College Cork.
How does our diet influence our microbiome (and what should we be eating more of to help our gut microbiome)? Do you think the current mental health crisis could be linked to our westernised diet?
Dietary patterns in Western society and elsewhere throughout the world have undergone major compositional changes, in recent decades, with the intake of red meat, high fat foods, and refined sugars vastly increased. This “Westernisation” of diets results in dysbiosis (also named dysbacteriosis), a term for a microbial imbalance or maladaptation on or inside the body (i.e. an impaired microbiota) that may at least in part contribute to the increasing incidence of stress-associated chronic inflammatory disorders, such as depression and anxiety.
Luckily, a solution is available for individuals looking for a healthy eating plan that is also beneficial to gut microbiome: the Mediterranean diet. The Mediterranean diet blends the basics of healthy eating with the traditional cooking methods and flavours of the Mediterranean. Furthermore, the Mediterranean diet was found to be associated with reduced risk factors for cardiovascular disease and is recognised by the World Health Organisation as a healthy and sustainable diet pattern. While there is no single definition of the Mediterranean diet – beyond a limited intake of red meat and processed foods – the main components typically include: the daily consumption of fresh vegetables, fruits, whole grains, nuts and seeds and healthy fats (e.g. olive oil), along with a regular intake of fish, beans, eggs, poultry and fermented foods. Other essential characteristics of the Mediterranean lifestyle are sharing meals with family and friends, being physically active and enjoying a glass of red wine.
Excitingly, the Mediterranean diet appears optimal from a mental health perspective. It is associated with lower rates of depression and appears to optimally impact on the gut microbiota with preliminary evidence indicating that such a diet may have antidepressant effects that have many positive benefits for stress-related psychiatric illnesses. Simply, truly good food does lead to a good mood.
What have been the breakthrough discoveries at APC so far (in rodents and/or humans)?
One notable study conducted at APC Microbiome Ireland, was a study showing that depressed patients had elevated cortisol output together with decreased faecal microbial richness. When rats were given a humanised microbiota from depressed patients, as opposed to healthy controls, they developed a depressive phenotype from both a behavioural and immune perspective. Thus, there was increasing evidence that some psychiatric disorders such as depression may be associated with a gut dysbiosis (i.e. a microbial imbalance). This study provided a breakthrough moment by providing compelling evidence for a role of the brain in regulating gut microbiome. Further, this study provided evidence that some psychiatric disorders, such as depression, have an association with a gut microbial imbalance that influences both mood and cognitive function, thus potentially highlighting one of the missing links that have restricted the pursuit of therapeutic advances in mental health medicine during the past years.
What’s your future outlook for psychobiotics?
The future outlook for psychobiotics is one that is positive due to the numerous benefits with minimal drawbacks. Although in context, while current narrative reviews, including this one, are largely enthusiastic about the field of psychobiotics – it must be noted that a recent systematic review of the psychiatric benefits of probiotics in humans found little evidence of positive outcomes. While this finding can be taken as in opposition to general optimism it does highlight that more research is needed to better understand and rigorously elucidate mechanisms that underpin the benefits of psychobiotics (i.e. prebiotics, probiotics).
By perhaps considering a wider definition of psychobiotics that incorporates dietary regimes (i.e. Mediterranean diet), we could then consider any substance that exerts a microbiome-mediated psychological effect, as potentially a psychobiotic. One further consideration should be in the methods employed to measure the psychological benefits and quantify potential confounds – the microbiome is sensitive to both diet and exercise, both of which affect mood and cognition, and both of which also affect vagal activity and as such would appear to share a signalling mechanism with other psychobiotics.
It is possible that the psychological effects of diet and exercise are partially mediated by the microbiome, and in this case, an argument may be made for them possessing psychobiotic properties. Future research should look to disentangle where possible the independent contribution of exercise, diet and microbiome upon mood and cognition in both an acute context as well as the more chronic adaptation. Differentiating the strength of effect of these subcomponents of a healthy lifestyle will help us better understand the interaction that exists both in the gut-brain-axis as well as in the human body as a system.