2. What led to your interest in researching the microbiota-gut-brain axis?

It was almost by chance. I was always interested in nutrition so I wanted to do that. When I started my degree at the University of Illinois, the lab was really focused on early-life nutrition and they were also looking at the microbiota. I was just really fascinated that the microbiota regulates almost everything in our body. It was mind-blowing to me that there is something else in us that can pretty much control us. I was always interested in the brain and had taken a couple of psychology classes at university. So I was very intrigued to  learn more about the gut-brain axis; I learned a lot by reading through literature, finding good articles and watching TED talks. All of this really got me excited about the gut-brain axis, which is how I ended up working here with John Cryan who is one of the leaders in the field.

3. You have undertaken research that focuses on the ‘psychobiotic diet’ and its influence on health, particularly mental health. Could you tell us what characterises the ‘psychobiotic diet’ and how is it different from other diets like the Mediterranean or Western diets?

Firstly, the reason why it’s called the ‘psychobiotic diet’ is because of John Cryan and Ted Dinan who coined the term. At first this term was focused on mostly probiotics but now really any exogenous factors can also be considered a psychobiotic. And so, when we started to think about doing a dietary approach, we were thinking, ‘What are the foods that we know benefit the (gut) microbiota?’ And that is how the ‘psychobiotic diet’ came about. It includes aspects of the Mediterranean diet like fruits, vegetables, whole grains, legumes and seeds, but also fermented foods, another big aspect of this diet. Thus, it differs from the Mediterranean diet in that way, another difference is that this diet does not focus much on the oils and fish. And of course, it is very different from the Western diet in that we ask participants to exclude a lot of unhealthy foods such as fried foods, high sugar foods, takeaways and so on.

4. You had recently delivered a presentation on the ‘Nutritional Modulation of the Microbiota-Gut-Brain Axis: Role of Diet in Cognition, Mood and Mental Health’ at the ‘Food for thought- – The role of nutrition in the gut-brain axis’ webinar for Love Your Gut – an initiative of Yakult. In your talk, you had briefly mentioned an ongoing study of yours that aims to assess the influence of psychobiotics on stress responses in healthy adults. Could you share with us some of the current findings from the study?

What is most exciting to us is that we found that people who followed the diet felt a prominent decrease in stress. Overall, they felt less stressed, more relaxed and had better sleep quality.  I think those are the most important preliminary findings we have. We are still looking at some of the biological analysis of the microbiota and what kind of role this could play. I can’t speak too much on that but finding the biological mechanism is very important. Seeing that it benefited the participants is already very exciting to us.

5. Based on our current understanding of the role of nutrition on the gut-brain axis, do you think we can expect to see nutritionists, dietitians and other health professionals using nutritional interventions to support the treatment or prevention of mental health disorders in the near future?

I think so, yes, as the whole area of Nutritional Psychiatry is moving forward.  There is very good evidence, especially from observational studies, linking good diet quality to better mental health, and it is known that eating a healthy diet will benefit your mental health and potentially decrease the risk of developing certain mental health disorders like depression. In my opinion the evidence to really establish  diet therapy specifically for patients  is still somewhat limited, as it is difficult to establish those evidence-based recommendations. However, even now, it sounds like psychologists include diets into the patient care as an additional add on therapy in the form of general healthy diet advice. It is not very detailed - simply telling them to eat healthy, eat fruits and vegetables and fibre etc. So it is already practiced a little bit but I believe this will become a lot more important in the future. Including dietary guidelines to support overall mental health can serve as a form of prevention rather than treatment so we don’t actually get to the development of mental health issues that require the use of direct treatment. Hence, we can prevent some of the development of these diseases.

6. In an article that you had published with your colleagues this year titled ‘Going with the grain: Fibre, cognition, and the microbiota-gut-brain-axis’, you reviewed studies investigating the link between dietary fibre and cognitive function, some of which reported health benefits that were associated with certain types of fibre. Do such findings suggest that we need to focus more on specific sources of fibre when it comes to nutritional interventions aimed at improving certain health conditions, rather than a general increase in fibre?

I think maybe in the distant future, yes. I think because we know how different fibres have different effects on health and the microbiota, we may potentially end up having more specific associations between fibre and aspects of mental health. Nevertheless, we still need to do a lot more research on that. Moreover, we know from the evidence that some of the more viscous fibres are important in metabolic health whereas fermentable fibres produce metabolites that have different effects on health. The more we get to know, the more we learn that the different protperties of fibre will be important.

7. I recently listened to the ‘Eat some bacteria’ episode of the BBC podcast ‘Just One Thing’ which you were featured in. With regards to your study which assessed the effect of the psychobiotic diet on mental health, you mentioned that some participants who previously followed a low fibre diet experienced gastrointestinal discomfort and flatulence initially during the intervention period. Do you think such experiences discourage people from increasing fibre in their diet? If so, is there a way to increase dietary fibre intake without experiencing these symptoms?

Yes, I think it definitely can be discouraging - nobody wants to have a stomach ache. One thing we did was to gradually increase the fibre intake of the participants instead of starting off with 30g of fibre per day. So increasing fibre intake gradually is very important. Also, in my study, we had 30 minutes every other week with the participants to assess their condition, so it was a little bit individualised. I think if people work with a dietitian, they can have one on one conversations to identify  which foods might be hurting your stomach or causing flatulence and sometimes these foods need to be substituted. So yes, I think it can be challenging but if you have the option to sit down with a dietitian, that can be easily managed. If you don’t have that option, gradually increasing your fibre intake and trying different sources of fibre is another option. Eventually your body will adjust. It might just take some time.

8. In your professional opinion, do you think it is more important to focus on diversity or the specific composition of the gut microbiota when investigating its beneficial effects on health?

It is a very difficult and interesting question because we are still trying to figure out what a healthy microbiota is. Some people say diversity is healthy i.e. having a lot of microbes is healthy. Some might argue, that if you have a lot of diversity, you might have some bacteria that are more pathogenic. Thus,  it might not always be that diversity is the best even though generally speaking, at the moment, diversity is still considered an indicator of healthy gut microbiota. I think eventually it will come down to function rather than composition – what does the microbiota actually do? It will be important to see if there is any functional redundancy so that different microbiota can perform different functions to allow us to digest fibres and polyphenols, for example. Furthermore, it is considered that if you have a stable microbiota it will be resilient to change such as, environmental stressors. So stability is also an indicator of a good microbiota. I hope at some point we can define what a good microbiota is but it’s very difficult to tell currently. Finally, we should consider how individualized our microbiota is. For example,  your microbiota might be super healthy for you but it might not be healthy for me. Generally, diversity is good and there is also beneficial bacteria like the ones in probiotics like Bifidobacterium and Lactobacillus.

It is also important to consider the population you are working with. For example, I used to work with kids with autism. In that sense, their high diversity [of microbiota] is not good because maybe some of the more pathogenic bacteria might contribute to their symptoms. Also, in infants during development, the diversity of their gut microbiota will be relatively low. If you compare breastfed to formula fed infants, we know that breastfed [infants] generally have healthy gut microbiota but their microbial diversity is not as high compared to infants that are formula-fed. This is because the diet of formula-fed infants is more complex which actually causes their gut to mature faster.

It is a million dollar question.

9. Do you have any advice for early-career researchers on how to maintain a healthy work-life balance whilst still making the most of as many opportunities as possible?

This is a very difficult one, especially in academia where you feel a lot of pressure to always do more. But it is very important to be able to shut that off. My tip would be to try and leave as much work in the lab as you can and  try not to get to emails on your phone during weekends. Put some time away for yourself where you say, ‘this is my time’. Otherwise, you lose the passion that you had, and that is one of the biggest things that will ruin your academic path. Having specific things that you do outside of work can help,  I personally like doing sports and I also enjoy cooking. Remember it is ok to not reply to emails straight away and it’s ok to do fun things.