By David Veale and Venetia Mitchell

Why we are writing this blog

Psychiatry is increasingly interested in the relationship between your gut and your brain. There are about 500 trillion bacteria, fungi and viruses living in your gut and we are only just beginning to explore how they can help you in your mental and physical health.

What we know

The ecosystem of bugs in your gut is called the gut microbiota (or gut microbiome) and its relationship with our brain is known as the ‘gut-brain axis’.

We are born with our own unique ecosystem of microbes that exist symbiotically with our bodies (this means we both benefit). How this ecosystem is made up is initially influenced by our mother’s microbiota. There is also some evidence to suggest that the way we are born (caesarean vs vaginal birth) can affect our microbiome.

As we age, we develop individual microbiome ecosystems. These can be influenced by a range of genetic and lifestyle factors. For example, eating lots of processed or junk food which are high in fat and sugar, lack of physical activity, smoking or antibiotics do not help the gut microbiota.

Our gut’s ecosystem has been shown to impact the levels of chemicals influencing the brain. This influences our mood. At the same time mental stress and low mood has been shown to negatively impact the balance of our gut microbiota.

Evidence from a range of sources is emerging to suggest that people with different mental disorders like depression or anorexia have distinct gut microbiota compositions. For example, studies that transplanted human gut microbiota from depressed patients into germ-free mice repeatedly find the mice become withdrawn and inactive. Researchers also see changes in the biochemistry of the mice brains.

What might a depressed human’s microbiome look like?

An imbalanced (dysbiotic) gut microbiome has been associated with depression. A depressed person is likely to have a low level of ‘beneficial’ species of bacteria and overall lack of diversity. Professor Felice Jacka in Australia did the first controlled trial that demonstrated eating a Mediterranean diet with vegetables and nuts was better for treating depression than social support. What we don’t know from this trial was whether the improvement was associated with changes in the gut microbiota. We especially need more research on the microbiome in OCD, BDD and other anxiety disorders. Imagine how in future you might be able to improve a mental disorder by altering your diet and gut microbiota. It’s never likely to be a cure but probably one part of the jigsaw.

So, what can we do to optimize the health of our microbiome and how do we know its status?

The Microbiome Test

The fastest way to determine the diversity and composition of your microbiota is to send off your faeces for analysis.  An increasing number of companies offer this. In the past I have used Atlas Biomed. The service costs about £150 and gives you a report on the composition of your microbiome. If you find you have a low microbiota diversity score, then the report can advise you how to alter your diet with more fibrous and fermented foods. I have a 9/10 diversity score and some pretty cool bacteria including Lactobacillus and Bifidobacterium.

The advice is personalized to your own ecosystem, recommending foods aimed to increase the diversity in your gut along with suggested fibrous and fermented foods that you are most likely to be able to break down effectively. You can download the Atlas Biomed app with clear guidance on making the small steps to updating your lifestyle habits which suit you best. We are also looking forward to downloading the Zoe app (Professor Tim Spector’s team) which will provide personalised feedback on your diet.

Getting the best optimal fibre and improving the diversity score of your microbiome might help improve your mental and physical health in the long term but this is still under research.

With or without a Microbiome Test…

If you do not wish to have your gut analysed, then there are straightforward dietary and lifestyle recommendations you can follow…

Dietary Recommendations

Scientists suggest that the optimal route towards gaining a healthy gut microbiome, and therefore a healthy gut-brain axis, is to consume a wide range of colourful, whole, plant-based foods (ie. real foods including fresh vegetables, pulses and legumes). To help understand why, it is helpful to learn about ‘prebiotics’ and ‘probiotic’ foods.


Probiotics: A healthy gut microbiome is made up of different live bacteria that provide benefits to our health and work with us in symbiosis. For example, many of them feed off the  fibrous foods we eat and create the Short Chain Fatty Acids that improve our mood. These beneficial species are called probiotics. Common probiotic microbes are members of the families, Lactobacillus and Bifidobacterium. You can read more here.

Examples of these probiotic foods are fermented foods such as sauerkraut, natural live yoghurts, kimchi, kefir, kombucha, miso soup, tempeh, sour pickles, fermented soft cheeses as well as commercial milks like Biomel. Probiotic foods introduce beneficial bacteria to help to enrich the diversity of our microbiota:  but don’t stick to the same ones all the time as diversity is important. A review by Wallace (2017) found that daily intake of probiotics   reduces depression and anxiety.

Prebiotics: Prebiotics are foods that nourish the beneficial gut microbes. Gut bacteria feed off prebiotic foods and transform them into beneficial substances for the body, for example Short Chain Fatty Acids. These may influence our gut-brain axis, improving our mood. Colourful, whole, plant-based foods tend to be prebiotic and have a lot of fibre. Dietary fibre comes from a range of plant-based carbohydrates that are not digested in our small intestine but reach the large intestine or colon where they are then broken down and utilised by our gut microbes. Because of this, fibre is an example of a prebiotic. Foods especially high in fibre include Jerusalem and globe artichokes, chicory root, asparagus, lentils, beans, onions, garlic, leeks, bananas, beetroot, broccoli, fennel root, wholegrain oats and barley.

Key to promoting and maintaining a healthy gut is ensuring diversity in your diet. It may seem overwhelming, yet research suggests we should aim for 50 different vegetables, legumes, grains, nuts, fruits and herbs per week. To start, it may be realistic to aim for at least 30 per week and here are quick tips on how to achieve this easily:

-When food shopping, seek to choose fresh herbs and vegetables you may not normally consume. Eating seasonally is a great way to do this easily. Wash vegetables but avoid peeling unless it is really required.

-Add an extra main vegetable to your plate.  If you usually have two, try having three.

-Enjoy the addition of herbs and spices to your dishes. A good simple set of cookbooks that I may recommend are by Rukmini Iyer’s, such as “The Green Roasting Tin”. They are simple one dish recipes which are easy to put together.

-Bulk buy nuts and seeds and, if possible, place them in containers on your kitchen side in order to sprinkle them on both savoury and sweet dishes throughout the day.

-Uncooked/ raw foods are better for higher fibre. If you are not used to consuming these foods, to avoid gut discomfort, it is recommended you start slowly and work on building up intake. It can also help some people to incorporate prebiotic supplements like Bimuno. Gut testing can help determine what fibre you might be missing.

Polyphenols: Polyphenols are natural chemicals found in many foods. They are designed to protect the plant and are also responsible for the bright and vibrant colours of fruits and vegetables. When we consume these colourful plants (often referred to as ‘eating the rainbow’) we gain antioxidant and anti-inflammatory benefits that help prevent illness and disease.

Our gut microbiota love these polyphenols too. Bugs in our gut transform polyphenols into bioactive substances. Polyphenols also promote the growth of beneficial gut bugs and as a result, they are considered prebiotics. An example of a food rich in polyphenols is dark chocolate with a cocoa content of 85% or above. Eat a square or two a day! A recommended supplier is Cocoa Runners. Other foods rich in polyphenols are green and black tea and berries.

Mental health benefits from consumption of such prebiotic polyphenols include reductions in stress, depression and possibly reducing the risk of Alzheimer’s. As so often, more research is needed but in a controlled study of older adults by Bowtell (2017) , just a quarter cup of concentrated blueberry juice a day improved cognitive function after 3 months.

Sourdough bread: In addition to consuming colourful, plant-based foods, a great way to gain both prebiotic fibre and polyphenols is to focus on good quality grains, such as a whole grain Sourdough bread.

Sourdough is baked using a natural yeast (also called “starter” or “leaven”) simply made from wholegrain flour, bread and salt. The process allows for a natural fermentation of the fibrous wholegrain. A long, slow fermentation of the dough lowers the amount of gluten and through the production of lactic acid bacteria, creates the ideal environment to promote the absorption of the nutrients from the wholegrain. All wholegrains contain gluten, and which in some people causes damage to the gut wall, promoting inflammation.

Sourdough bread is a great way to lower any negative effects a standard, refined industrially made bread may cause and, at the same time, boost your intake of quality prebiotics. Ideally however, home baking is recommended to guarantee a long fermentation (how long you leave your dough to sit).

If you are new to baking and the concept of sourdough bread, we recommend The Sourdough School. You can join their Sourdough Club to understand, learn and find out more about why sourdough may boost your mood. Online tuition, deeper understanding and a supply of recipes are provided.

Are you keen to read more on food and mood?

You can read about the emerging science for the gut-brain axis in the book “The Psychobiotic Revolution” by Scott Anderson. A good overview on the role of diet and the brain is found in the book by Professor Felice Jacka: “The Brain Changer”. If you are really interested in this area, I also recommend reading books by Professor Tim Spector, including “The Diet Myth” and “Spoon-Fed”.

In a second blog, we will provide more on the science and in our third blog specific advice on what to eat.

Lifestyle Recommendations

Intermittent Fasting

Eating three times a day at set times can help you be in sync with your circadian rhythm – although getting up with the light by 7:30am is a more powerful way of synchronising your circadian rhythm and can improve your microbiota. A diet with a gap of 16 hours between eating that can help improve your gut microbiota (and lose weight).


Regular exercise has shown to have an anti-inflammatory effect suggesting this improves the home for our gut microbiota by supporting gut wall integrity. Excessive exercise however has been shown to have opposing effects, by increasing inflammation and affecting the gut wall strength. It is recommended that you find a level of movement that suits you personally, and make it regular and habitual in order to support the gut microbiota and ultimately improve your mood.

Note: There are three blogs in this series. Find out more about Understanding the Microbiota-Gut-Brain-Axis: The Science in the second blog. Discover how Eating nutrient-dense foods might improve your brain health in the third blog.

References/Further Reading and Listening:

Atlas Biomed

BMJ 2020;369:m2382 Review on the role of diet in mood

Bowtell JL, Aboo-Bakkar Z, Conway ME, et al. Enhanced task-related brain activation and resting perfusion in healthy older adults after chronic blueberry supplementation. Appl Physiol Nutr Metab. 2017;42:773-779.

J Nutr Metab. 2020; 2020: 5631762. A Review of the Science of Colorful, Plant-Based Food and Practical Strategies for “Eating the Rainbow”

Nutr Clin Pract. 2015 Dec; 30(6): 734–746 The Gut Microbiome: What we do and don’t know

Prof John Cryan on Dr Chattergee’s Feel Better, Live More (E.20)

The Sourdough Club

Wallace CJK, Milev R. The effects of probiotics on depressive symptoms in humans: a systematic review.Ann Gen Psychiatry. 2017;16:14.