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Gut health explained: what it is and how to improve it

woman in a black jumper sat at a table
9 min read
AUTHOR: Kaitlin Colucci
Gut brain connection illustration

When you type ‘gut health’ into Google, you get more than 1 billion results returned. From books, to blogs, to the BBC – everyone is talking about gut health.

The gut is referring to the function of the entire gastrointestinal (GI) tract. The GI tract starts at the mouth, and finishes…down the exit at the other end. So includes your oesophagus, stomach, small intestine, large intestine, rectum and anus.

The main function of the gut is to absorb nutrients from the food we eat, whilst also ridding solid waste from the body. As well as this, the gut also hosts a huge number of bacteria – both good and bad, which is better known as the gut microbiome.

Approximately 100 trillion micro-organisms exist in the human GI tract, and these can all aid with digestion of nutrients, support a healthy immune system, and more recently have even shown a link between stress, anxiety, insomnia, and weight gain via something called the Gut-Brain-Axis. This is essentially a pathway in which the gut talks to the brain and vice versa.

There is no universal definition for ‘good gut health’ and no two people’s gut microbiota are the same. The absence of gut symptoms such as bloating, constipation, diarrhoea, excess flatulence, abdominal pain etc. may be an indicator of good gut health. However, research has shown that 1 in 3 people suffer from one or more of these symptoms.  

What sort of factors may influence our gut health?

Studies looking at human twins have shown that although there is a heritable component to the gut microbiota, there are many factors that independently influence its composition.

There are many causes for this, some of which can’t be helped such as ageing and becoming ill. However, stress, unhealthy dietary habits, unnecessary antibiotics, mood, sleep and smoking are among the causes that can be helped.

Lifestyle factors such as stress and sleep have been shown to have a significant impact on the gut bacteria, which may explain the association between lack of sleep and weight gain. We all become ill at times when antibiotics are a necessity, but avoiding antibiotics unless absolutely necessary, saves healthy gut bacteria from being wiped out and causing long term changes to your gut microbiota.

Healthy eating is also key to good intestinal health. Studies have shown that eating a diet low in fibre and high in processed foods has been linked with alteration in gut microbiota and increased chronic disease risk. A variety of plant foods are necessary to have a variety of strains of good bacteria in the gut.

How to improve gut health

1. Eating 30 plant points per week

It is now well known that a diet rich in plant diversity can increase the diversity of the gut microbiota the trillions of bacteria that live inside the large intestine. The American Gut Microbiome research found that those who ate 30+ different plant-based foods per week had a far more diverse gut microbiome compared to those who ate less than 10 plant foods per week. This is important as a more diverse gut microbiome is associated with better gut health. Having a wide variety of microbes in our gut makes our microbiome more capable and resilient.

Plant based foods (e.g. fruit and veg, wholegrains, cereals, pulses, nuts and seeds) are rich in dietary fibre which cannot be broken down by the body and so pass through the digestive tract to the large intestine. Here, the gut bacteria attempt to break down fibre through a process known as fermentation. High fibre intake encourages the growth of species that ferment fibre into metabolites known as short-chain fatty acids (SCFAs). SCFAs have a myriad of benefits to the body including improved immunity, blood–brain barrier integrity, can have a protective role against types of disease such as type 2 diabetes and inflammatory bowel disease, and can help regulate the function of the intestine, as well as brain, and other organs in the body.

However, make sure to make gradual changes to start as a sudden increase in fibre in your diet may cause bloating, tummy pain, and/or constipation or diarrhoea.

·   Increase slowly: gradually increase your plant intake over a few weeks so that you’re hitting those 30+ plant points each week. Start with half the portion size of the fruit, vegetable, or beans you think bloats you and gradually increase up to a full portion over a few weeks.

·   If beans and lentils are the problem: make sure to focus on increasing your intake of other plant based proteins such as nuts, seeds, tofu, and high protein grains. Choosing tinned beans and pulses, and thoroughly rinsing them before eating can help with their digestion. And keep to no more than around 100g per sitting.

·   Relax: stress can increase the sensitivity of the gut via the gut-brain axis. Do some box breathing exercises or a gut-directed yoga flow which can help to relax the gut muscles and therefore reduce the sensitivity of the gut.

Do you have to eat a vegan diet to increase gut microbiome diversity?

A vegan diet is defined as one that eliminates all animal foods and products such as meat, fish, shellfish, insects, dairy, and eggs, and is rich in many plant-based foods. However, although plant-based foods increase your gut microbe diversity, you can still increase your plant intake whilst consuming dairy and animal products, so the choice is yours!

2. Reducing intake of ultra-processed foods

Experts have long raised concerns about the link between ultra-processed foods and poor health. More research is now linking the effect of these foods on our gut health too.

Foods are processed in many different ways and can have some benefits such as making a food more digestible, improve its flavour and appearance, remove harmful bugs or toxic substances, and can make food last longer. In its simplest form, cooking raw food is a form of processing, as is grinding wheat into flour, or pasteurising milk to kill harmful bacteria.  We have been roasting, baking, boiling, freezing, chopping, grinding, drying, pressing, canning, smoking, salting, and sweetening our foods for a very long time.

However, in the last few years, there has been an increase in what are known as ultra-processed foods which often contain lots of added sugar, fat, salt as well as many other chemicals, preservatives, and emulsifiers, and are linked to metabolic changes and poorer health.

Ultra-processed foods are made mostly from ingredients that have been highly modified such as high-fructose corn syrup, together with additives such as preservatives, antioxidants, and stabilisers. The foods which contain these types of ingredients are foods such as cakes, cookies, fizzy drinks, ready meals, and ultra-processed snacks.

Ultra-processed foods and drinks can contain high levels of refined carbohydrates, saturated fats, salt, and chemical additives. In addition, they often lack dietary fibre (which we know is important for good gut health), good sources of protein, and healthy fats.

Eating a high intake of ultra-processed food is associated with being overweight and having worse health outcomes, conditions such as heart disease, type 2 diabetes, irritable bowel syndrome, depression, asthma, and cancer. The latest findings from the PREDICT study found a strong association between eating a diet rich in minimally processed plant-based foods and having more species of ‘good’ gut bugs.

Interestingly, the study found that diet quality, including the proportion of processed versus unprocessed foods, was just as important as the type of food themselves. For example, processed animal-based foods like sausages, bacon, and creamy desserts were associated with having more ‘bad’ microbes, as might be expected. But highly processed plant-based foods such as juices, sauces, and baked beans were also associated with ‘bad’ microbes, highlighting how important food processing is for our microbes and our health.

3. Stress management

The gut and the brain are constantly communicating to each other via a pathway called the gut-brain axis. This communication is through the:

  • ‘Rest and digest’ (parasympathetic) nervous system, and the…
  • ‘Fight or flight’ (sympathetic) nervous system

These nervous systems communicate with the gut via the vagus nerve. When we are stressed, our brain sends signals to our body to tell us that we are stressed. The parasympathetic nervous system slows down, and the sympathetic nervous system switches on. All the blood rushes to our muscles to get them ready to fight. This can lead to several different things:

·   Constipation: with less blood flow to the gut muscles, some can find it more difficult to pass a bowel motion.  The speed at which food passes through the gut can decrease, leaving more time for water to get reabsorbed from your poop, leaving you with dry hard poop. Due to the decreased time at which things move through the gut, you may not pass a bowel movement at all.

·   Diarrhoea: for some, stress can also increase the speed at which things move through the gut, and increase fluid secretion. This leads to frequent and loose bowel movements.

·   Abdominal pain: stress can also cause increased sensitivity of your intestine, a term called visceral hypersensitivity, which we see particularly in those with functional gut disorders like irritable bowel syndrome (IBS). This can lead to abdominal pain and bloating through the connection between the gut-brain axis.

Stress management including breathing exercises, meditation, yoga or any other forms of exercise, spending time in nature and taking time for self-care can all help stimulate the parasympathetic nervous system, reconnecting the gut and brain and decreasing the sensitivity of the gut.

Which foods can improve gut health?

As well as aiming for 30 plant foods per week, there is now more emerging evidence for the use of fermented food in our diet to maintain a healthy gut. This includes foods such as kimchi, sauerkraut, kefir, kombucha and miso to name a few. Fermented foods contain natural probiotics which are beneficial microbes that can increase the balance of good bacteria in the gut. Scientists from the University of California San Diego have been looking at whether eating fermented foods alters the gut microbiome. They found that those who consumed fermented foods a few times per week had a subtle but statistically significant difference in their gut microbiome, favouring the ‘good’ gut microbes in the gut. Fermented foods can have a unique flavour, so my recommendation is if you’ve never tried them, then definitely give them a go!

Good gut health

There is no universal definition for good gut health but there are several things we can do to look after our gut health. It’s all about feeding our microbes a wide variety of foods, decreasing our intake of unhealthy foods, and managing life’s stresses to reconnect the gut and brain.


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