Get to know your gut microbiome: what stories do your gut bacteria tell?

The human gut includes a complex ecosystem of micro-organisms, including bacteria, archaea, eukaryotes, fungi and viruses. It’s estimated that the gut microbiome of a healthy adult acts as host for almost 2000 different species of bacteria and around 100 trillion micro-organisms. These micro-organisms all have genetic code that enables the expression (turning “on” or “off”) of over three million unique genes. We have other microbiomes in places where our body comes into contact with the outside world (mouth, skin, nose, and vagina) all uniquely adapted to living in these different environments but this article will focus on the gut microbiome.

The gut microbiome weighs an estimated 2kg and acts as an intermediary between the food we eat and how our body functions. It’s the best researched of all the microbiomes, largely because it’s easiest to access via a stool sample. You may be surprised to find out that 25 – 54% of your stool is made up of bacteria (both dead and living).

The impact of having low bacterial diversity in our gut

deforestation and trees chopped down in a forest to represent low bacterial diversity in the gut

Whilst we still have much to learn about the gut microbiome, researchers are in agreement that, just like a rainforest, a healthy gut is one with a wide range of species (different types of bacteria rather than different types of plants!).

Lower bacterial diversity has been observed in people with many types of health conditions including inflammatory bowel disease, psoriatic arthritis, type 1 and 2 diabetes, atopic eczema, coeliac disease, obesity and arterial stiffness. The composition of our gut microbiome also impacts our individual blood sugar response to different foods. It’s thought that our gut bacteria modulate our risk of many chronic diseases including inflammatory bowel disease, obesity, type 2 diabetes, cardiovascular disease and cancer.

Listen to your gut – what do gut bacteria do?

coloured paper clips linked in a chain to represent short chain fatty acids

Our gut microbes carry out a multitude of tasks including communicating with our immune systems, protecting us from pathogens (bugs that can induce disease) and assisting us in accessing nutrients and energy from food.

This includes taking the dietary fibre that we eat, a type of carbohydrate, and fermenting it to produce short chain fatty acids (SCFAs) like butyrate.

Butyrate is particularly important for helping to maintain the intestinal barrier and has been shown to have many health benefits both in the gut and elsewhere in the body.

Historical and global variations in our gut microbiome

a caveman standing in the forest to illustrate how our gut microbiomes differ from that of our ancestors

One of the key functions of our microbiome is to digest certain carbohydrates that we can’t, not just any type of carbohydrate but specifically microbiota-accessible carbohydrates (MACs). MACs are complex carbohydrates, the types found in vegetables, fruits wholegrains, nuts, seeds, and legumes. Western diets are very different to that of our ancestors. For over 200,000 years most humans were foragers with diets high in plant material. As a result, researchers suggest that their gut bacteria were well adapted to consume MACs and produced high amounts of SCFAs.

During industrialisation, a combination of lower consumption of MACs, increased consumption of protein, fat and sugar, increased exposure to chemicals (in processed and intensively farmed food) and medications (such as antibiotics) has probably led to a deterioration in the diversity of our gut microbiome. A modern western microbiome is likely to have much lower diversity with lower amounts of SCFA producing bacteria.

Globally, there are variations in gut microbiomes. In Japan where seaweed has traditionally been an important part of the diet, the Japanese are able to digest seaweed with the help of their gut bacteria. This ability isn’t present in the average Western gut microbiome.

What does a disrupted gut microbiome look like?

A rusty leaky pipe to illustrate intestinal permeability, known as "leaky" gut.

An unhealthy gut microbiome is often described as being in a state of dysbiosis. This tends to mean there’s a less diverse and less stable community of bacteria, which may make it easier for certain strains of bacteria to dominate the gut and beyond. This may activate inflammation both in the gut and elsewhere in the body. Gut microbiome dysbiosis has been linked to many conditions including several autoimmune diseases and anxiety and depression.

The intestinal barrier covers a surface area that for some is considered to be equivalent to the that of a tennis court and for others, half a badminton court. Either way, it’s a large area for the immune system to police! It helps us to regulate the absorption of nutrients, electrolytes and water from the gut and keep out potentially harmful substances. This is composed of a mucus layer on top of a single layer of cells called epithelial cells, which are joined together by tight junctions. These tight junctions help control what passes through the epithelial cells.

This intestinal barrier can be altered by our gut microbiome leading to increased intestinal permeability. Many diseases have been associated with increased intestinal permeability including inflammatory bowel diseases and other psychiatric disorders including depression and anxiety.

Why your gut microbiome might not be in the best shape

Birth

Whether you were born through vaginal delivery or caesarean will have an impact on your gut microbiome. During a vaginal birth, microbes are transferred from the mother’s vaginal microbiome to the baby. Babies born via caesarean section don’t have this exposure to the vaginal microbiome and their gut microbiomes are more likely to include skin and oral microbes and even bacteria from the operating room. Children born via caesarean are more likely to develop asthma and allergies and the microbiome differences persist even in adulthood.

Exposure to antibiotics

We’re exposed to antibiotics not just when prescribed them by a doctor but also through their use in farm animals and crops. Our gut microbiome is changed by exposure to antibiotics, leading to a depletion in bacterial diversity. Research has found that antibiotic exposure can lead to changes that promote long term disease and foster bacterial resistance.

Genetics

Research has found that some of the composition of our gut microbiome is down to our genetics. The bacterial species Christensenellaceae (which is associated with a lean BMI), is one of the most dependent on genetics.

Diet

Just like humans, bacteria need to eat to survive. A diet high in processed food and low in plant fibre is likely to lead to an unhappy gut microbiome, lacking in diversity. Researchers have found that the environment created in the gut by ultra-processed foods (typical of a Western diet) favours microbes that can promote diverse forms of inflammatory disease.

Artificial sweeteners and food additives

Research is ongoing but artificial sweeteners and food additives, such as emulsifiers have been shown to negatively impact the health of the gut microbiome. Emulsifiers are incorporated into many processed foods to improve texture and stability. They’ve been shown to shift the gut microbe population and increase low grade inflammation increasing the risk of colon cancer in mice. However, the relevance to humans remains uncertain.

Exposure to chemicals

Exposure to environmental chemicals has been shown to cause alterations in the gut microbiome. This includes pesticide exposure, chemicals in cookware, food packaging, furniture, toys and chemicals in our air and water. Whilst we’re unable to completely eliminate our exposure to these, there are things we can do to minimise our exposure.

Can I do anything to support my gut microbiome?

healthy plant based foods that are good for gut bacteria

Absolutely! The good news is that scientists have found that of all the environmental factors they’ve studied so far, diet has the largest impact on the gut microbiome. Dietary considerations include:

  • Enjoying a diverse diet that’s high in plants like salad, vegetables and herbs will support a health promoting microbiome. This includes vegetables, legumes (peas, beans, and pulses) fruits, nuts, seeds, fruits, and wholegrains. The American Gut Project found that people who eat more than 30 different plant based foods a week tend to have far greater microbial diversity and SCFA producing bacteria.
  • Eating a diet low in processed foods. This means avoiding processed and ultra-processed foods and drinks that can contain high levels of refined carbohydrates, factory-produced fats, salt, and chemical additives and lack dietary fibre, quality sources of protein, and healthy fats ( like avocados, salmon, olive oil, raw nuts and seeds).
  • Include fermented foods and drinks. Fermented foods and drinks such as yoghurt, kefir, sauerkraut, kimchi and miso are likely to have a beneficial impact on health and the gut microbiome.
  • Eat a diet rich in polyphenols. Polyphenols are compounds found in plant foods, including in wine, tea, apples, raw cacao (the raw unprocessed form of cocoa), coffee, berries and extra virgin olive oil. Our gut bacteria help us to absorb these polyphenols and they positively impact the composition of the gut microbiome. Polyphenols increase the abundance of a beneficial bacteria called Akkermansia muciniphila.

A checklist of plant-based foods to help people get 30+ a week to improve their gut health.

You can download the handy plant-based foods checklist by hitting the button below. Why not print it off and stick on your fridge as colourful inspiration when you’re planning your meals for the week ahead?

Other things to consider include:

Little girl asleep on a dog to illustrate the fact that pets might be good for your gut microbiome.

a plate with a knife and fork on top of it and the words 'gut health' overlayed on top of it.

Whilst there may sometimes be a place for intervention beyond food changes, such as anti-microbials, probiotics and other supplements, weaving in gut-friendly foods can go a long way in supporting our microbiome. Now you know what an important role these microbes play and how fundamental they are to your health, why not give your diet a few tweaks to make sure you’re supporting the bacterial diversity of your gut?

Did you know lightbulb icon in a circle with a green border

If you haven’t already done it, our Gut Microbiome Check in the Records section of the Evergreen Life app offers you an opportunity to identify factors from both your early years and present life that could have impacted the balance of your gut microbiome – some may surprise you! We’ll also steer you towards adjustments you can make to help you optimise your gut microbiome for health – many of which you can enjoy solo or with friends and family.

If you don’t have the questionnaire in your app yet, make sure to look out for a notification.

Reviewed by:

Dr Brian Fisher MBBch MBE MSc FRSA – Clinical Director

Nicky Verity MSc BSc – Wellbeing Researcher

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Picture of  Ingrid Kitzing

Ingrid Kitzing

Ingrid Kitzing is a nutrition expert here at Evergreen Life. She trained as a Nutritional Therapist at The College of Naturopathic Medicine, and is passionate about helping people bring healthy and nutritious food into their lives.

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