You may already believe that many of your behaviours and choices – smoking cigarettes, having a few too many drinks, or routinely choosing Netflix over the gym – can impact your health in a big way. Researchers are starting to understand how some of these factors influence the types of microscopic organisms that live and thrive in our guts. Some factors that contribute towards your gut-body-and-brain health are determined around conception, such as your parents’ genetics and lifestyle, the environment you’re born into and exposure to infection or illness. The contribution of these on your health is fairly stable, yet your gut microbiome undergoes many changes throughout your life and these changes may influence your health. Fortunately, there are behaviours and habits that you have control over that give your gut microbiome the best chance of being healthy and well-functioning. Of the factors that you can control, lifestyle, including diet is key to determining what lives and thrives in your gut. This is important, of course, because everyone eats!
What does the research say?
Asking large groups of people to follow a very strict diet while having their blood and bodily functions closely monitored is a complicated undertaking. Because of this, many of the studies on diet and the gut microbiome have been done in animals, where it is much easier to closely monitor changes in their biology – and of course, they are much less likely to complain about eating the exact same thing several nights in a row!
Many studies have looked at the impact of diet in determining the population of our gut microbes, and scientists (including us at the Food & Mood Centre) are starting to think about what this means for health and disease. Studies have shown that as areas with traditional diets become more urbanised, their microbiome compositions shift in line with their dietary habits. Similarly, a study compared the diets and gut microbiomes of urban and traditional communities in Bangladesh. The Bengali people in the study were consuming more meat, rice, and fried foods, whilst the indigenous people were consuming a diverse, seasonal, foraged diet. This study found the indigenous populations tended to have a higher Firmicutes to Bacteroides ratio, a microbiome marker traditionally associated with better health outcomes.
It seems that what we eat regularly over a long period of time influences the diversity, type, and roles of the microbes that live in our gut. A healthy diet is associated with a richer and more diverse gut microbiome – a good thing in terms of supporting your immune system, reducing inflammation and regulating other systems in your body and brain. However, at this point it is difficult to say exactly what a ‘healthy gut’ looks like, other than it is able to function properly.
How quickly can the gut change?
Several studies have shown gut microbes can change quickly and dramatically when dietary changes are made and when antibiotics are administered – sometimes as quickly as within 24 hours. At this point, most of these studies have been conducted in animals, with only relatively small human studies so far. For example, researchers in Canada have shown that gut microbiome composition could change rapidly in response to a three day Mediterranean diet intervention, but that many beneficial changes could be reversed when participants were put on a standard Canadian diet for 13 days. When participants were returned to the Mediterranean diet for another three days, changes were even more pronounced, but not all changes from the Canadian diet could be reversed in this second round of Mediterranean diet exposure. Importantly, a fascinating study in which rural Africans and African Americans swapped diets showed that profound changes in markers of cancer risk in the bowel, and microbial cancer markers, were evident within only two weeks.
These findings are important, because they show that diet has the ability to quickly shift the type of bacteria in your gut. However, it’s important to note is that in most cases, the gut microbiome returned to ‘baseline’ after the studies ended, highlighting that you need to consistently eat a healthy diet to make lasting change to your microbes. Overall, it seems that a old-fashioned good-quality diet, rather than short stints of ‘dieting’, is best for improving and maintaining a healthy gut.
What does this mean for my brain and mental health?
Our gut and brain are connected through several different pathways – you may know this to be true if you’ve ever felt butterflies in your stomach when you’ve been nervous or scared. Interestingly, diet is also related to many of the systems that help your brain and gut communicate (for example, the immune system and the protection and survival of healthy brain cells). When you consume a healthy diet – one that is rich in whole plant foods – your digestive system breaks these foods into smaller components that your body can use to keep it functioning optimally. In particular, when you eat and digest fibre rich foods (think whole grains, fruits and vegetables), your gut microbiome produces by-products called Short Chain Fatty Acids (SCFAs) that help to reduce inflammation. Eating a good quality diet can also help to keep the barrier of your intestinal wall intact, avoiding ‘leaky gut’.
On the other hand, eating a poor quality diet can increase your risk for common mental disorders like depression and anxiety. Eating more ultra-processed food has been shown to be associated with elevated distress and other adverse health outcomes including mental disorders. Some dietary patterns are associated with the level of inflammation throughout your body, and pro-inflammatory diets are associated with increased risk for depression. Your gut microbiome may play a role as a messenger between an unhealthy diet and the regulation of your mood.
What can I do?
Happily, there is good evidence that our diets can affect, and even protect, our mental health and one of the ways is through your gut microbiome. Eating a diet rich in fibre, colourful plant foods and pre and probiotic foods may have many benefits for the gut and subsequently for the brain. A habitual, healthy, whole food diet can help to promote the health and diversity of our gut bacteria by breaking down fibre into by-products that help to reduce inflammation, and this also helps to keep the gut barrier healthy and intact. Targeting your gut health by eating a healthy diet might reduce some of the risk factors that are associated with common mental disorders.
In summary
Your lifestyle choices, particularly diet, play a significant role in shaping your gut microbiome, which in turn impacts both your physical and mental health. By consistently maintaining a healthy, whole-food diet rich in fibre and plant-based foods, you can support a diverse gut microbiome, potentially reducing the risk of mental health disorders and promoting overall well-being.
