Gut Microbiota and Diet

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 on your health in a big way. Researchers are starting to understand how some of these factors influence the types of bugs 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 microbiota 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 sneak out for dessert.

Many studies have looked at the impact of diet in determining the population of our gut bacteria, and scientists (including us at the Food & Mood Centre) are starting to think about what this means for health and disease. A key study, conducted by De Fillipo and colleagues examined the gut bacteria of European children, and compared with kids who grew up in rural Africa. The diets of the two groups were quite different; European children consumed more processed or ‘Western’ foods compared to the largely plant-based diet of the African children. Amazingly – and perhaps not surprisingly – the bacteria living in the guts of these children were completely different. The African children were found to have more types of bacteria overall, many of which are anti-inflammatory, meaning they help to combat harmful inflammation that increases risk of disease. Some of the healthy bacteria living in the African children’s bellies were nowhere to be found in the Europeans; they simply had fewer types of bacteria.

It seems that what we eat regularly over a long period of time influences the ‘type’ or cluster of bacteria that live primarily 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 microbiota 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 the UK, have shown that your gut microbiota are changed quite quickly when your diet is altered (such as altering carbohydrate, protein intake or the types of fibre consumed). Another study of ten individuals who were assigned to either a ‘plant based’ or ‘animal based’ diet recorded dramatic changes to their ‘gut profiles’ after just five days of their new diet. 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 were evident within only two weeks (the poor rural Africans experienced an increase in these markers, and the African Americans a reduction).

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 bacteria. Overall, it seems that a good 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 fruits, vegetables, nuts, pre and probiotic foods and fibre – 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, starchy vegetables), your body 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 highly processed junk food has been shown to be associated with a smaller hippocampus – a critical part of your brain that is responsible for learning and memory, as well as regulating mood.  It can also encourage a constant, low level of inflammation throughout your body. These are risk factors for mental illness, and the gut bacteria 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 microbiota. Eating a diet rich in fibre, colourful plant foods and pre and probiotic foods like onions, garlic, Jerusalem artichoke, kombucha and yogurt, 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 nice healthy diet might reduce some of the risk factors that are associated with common mental disorders (while also benefiting your physical health). If you’re in control of your diet and interested in tweaking it then a good place to start may be cutting down on ‘discretionary foods’ (if you eat them), and gradually increase your intake of fibre!