Gut health

Written by Katherine Nicholls
Katherine Nicholls
Nutritionist Resource Content Team

Last updated 18th July 2022 | Next update due 17th July 2025

Nutritional therapists can support people struggling with gut health issues and digestive conditions by providing expert guidance and a tailored approach to make safe and effective changes to diet and lifestyle.  

What does the gut do?

The gut (also known as the digestive system, gastrointestinal tract or gastrointestinal system) is made up of a group of organs: the mouth, oesophagus, stomach, small intestine, large intestine, liver, pancreas and gallbladder, and is home to your unique gut microbiome (GM).

The gut's primary functions are to absorb nutrients from the food we eat and excrete waste. The body will use the nutrients containing vitamins, proteins, fats and calories in order to carry out essential jobs around the body that contribute to a person’s overall physical and mental well-being. 

The gut, when it’s healthy, can work harmoniously, but when it has a bacterial imbalance – also known as gut dysbiosis – it can lead to unpleasant, physical symptoms. Aside from gut bacteria, some people may suffer from long-term inflammatory digestive disorders or autoimmune disorders of the gut such as Crohn's disease or ulcerative colitis and may also benefit from nutritional therapy.

There is also a growing body of evidence that suggests what we eat and the health of our gut microbiome (directly related to our food intake and lifestyle) can have a significant impact on our mood and even the prevalence of a mental health condition. 

Nutritionists who can help with digestive issues

The gut microbiome

The gut microbiome bacteria are represented by three different groups:

  • good/beneficial bacteria
  • potentially harmful bacteria (if the right environment)
  • bad/pathogenic bacteria

Our gut microbiome or GM is unique to each individual and quickly develops a neurological network that sends messages to the brain, through the vagus nerve connecting the gut and brain. Not only is it physically connected to the brain, our GM also influences our immune system function, our weight and problematic digestive issues such as irritable bowel syndrome.

Your gut microbiome is fragile and with modern-day advancements and busy lifestyles encroaching on our health, sometimes the gut microbiome takes the brunt. For example, if you have been on a prolonged course of antibiotics, your good and bad bacteria may both have been killed off by the medication.  

Functional medicine practitioner and nutritionist Rosie Letts (BSc Hons, MBANT, CNHCs) suggests replenishing your gut bacteria with healing foods such as homemade bone broth, protein and fermented foods (miso, sauerkraut, kefir etc.).

Homemade bone broth is an incredibly nutrient-dense food that is packed with gelatin, l-glutamine and collagen which soothe the digestive tract, repair damaged cells and improve nutrient absorption

- Rosie Letts (BSc Hons, MBANT, CNHCs) 

How does the gut work?

Food moves through the gut in five main progressive stages:

  1. Mouth – In the mouth, the teeth begin the digestive process by tearing and grinding solid food into sizeable pieces. Saliva then begins to break down the food into enzymes. 
  2. Oesophagus – The soft mass of chewed food in the mouth is then swallowed. The oesophagus (tube leading to the stomach) squeezes the partly digested food to the stomach by contracting in a wave-like motion known as peristalsis. This process takes less than six seconds. 
  3. Stomach – The stomach muscles contract to mix the food with hydrochloric acid and digestive enzymes, secreted from the gastric glands. These digestive juices break down the proteins, sugars and fats found in food.
  4. Small intestine – The partly digested food is then squeezed from the stomach through the duodenum and into the small intestine. Here, bile from the liver begins to emulsify fat and digestive juices from the pancreas continue to digest nutrients. Villi on the wall of the small intestine increase the surface area and aid the absorption of smaller molecules into the bloodstream.
  5. Large intestine – By the time the food leaves the small intestine, most of the nutrients will have already been absorbed. Next, the resulting lump of mostly digested food moves slowly through the colon. This is the last stage of absorption, leaving only a mass of fibre and bacteria. Because this mass of waste cannot be used by the body, it is finally excreted through the anus.

Common gut health issues

A gut health problem is a change or abnormality in the natural functioning of the digestive process. Problems with your gut health or digestive conditions are extremely common. As many as 40% of the UK population suffer from at least one symptom of a digestive problem at any one time and can negatively impact a person’s quality of life.

The terms gut health problem or digestive condition cover a large variety of conditions, symptoms and diseases that affect your gut.

Types of digestive problems:


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Crohn’s disease

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Ulcerative colitis

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’Leaky gut’ syndrome

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'Leaky gut syndrome'

Leaky gut syndrome is a proposed digestive health condition that proponents suggest can lead to a wide range of long-term health conditions, notably autoimmune diseases, such as multiple sclerosis, lupus and chronic fatigue syndrome. 

It's thought that leaky gut syndrome, also referred to as increased intestinal permeability, is caused by the immune system having an adverse reaction to toxins and bacteria that have been released into the bloodstream via a porous bowel.

This happens when the inside lining of the bowel (mucosal barrier) – made up of a single layer of cells separating the gut from the body – becomes less effective, and allows large molecules and germs from the bowel to enter the bloodstream. This barrier is usually effective in absorbing nutrients and protecting pathogens from entering the bloodstream.

More research is needed to determine if a porous bowel is actually the cause of leaky gut syndrome, rather than other conditions, medications or lifestyles causing the condition.

Can digestive problems be serious?

Most digestive problems are very mild and can be cured quickly and easily with the help of a nutrition professional or managed with diet and by taking appropriate medication.

However, some gut health problems are considered to be very serious and vary in cause and are not related to your gut microbiome. These can be diagnosed by identifying ‘red flag symptoms’. You can ask five simple questions to help identify red flag symptoms:

  • Have you noticed a sudden and drastic change in the functioning of your bowels?
  • Have you recently lost weight for no reason?
  • Do you have difficulty swallowing?
  • Have you noticed an increase in heartburn or stomach pain?
  • Have you noticed bleeding from your back passage?

If you experience one or more of these symptoms, it is advisable to visit your GP.

Gut health and your mental health

The gut has often been dubbed ‘our second brain’, and the phrase “that gut feeling” may have more truth to it than we originally thought. Several studies have suggested that gut dysbiosis could contribute to feelings of low mood and even mild depression. 

Scientists refer to the gut-brain connection as the microbiome-gut-brain axis, a chemical pathway using neurotransmitters to send direct messages between the central nervous system and the gut. 

Certain species of bacteria found in a healthy GM aid the production of neurotransmitters in the brain such as serotonin, our happy hormone and it’s estimated that 90% of serotonin is made in the gut. If our gut bacteria is out of balance, we may struggle to regulate our moods.

Want to know more about the gut-brain connection? Harley Street nutritionist Rhiannon Lambert explores the food and mood connection on the I am. I have podcast.

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How can a nutrition professional help with gut health?

Good nutrition and professional guidance can support your gut health in a number of ways, whether diagnosed with a condition or not.

In your first session, a nutrition professional will discuss your symptoms, diagnosis (if applicable), lifestyle and dietary choices, plus work through your relationship with food to gain a clear picture of your current diet. They will make recommendations if further investigation is needed - such as tests that GPs can organise - and work with you to draw up individual, tailored plans that support a diagnosis or unpleasant symptoms.  

With nutrition and diagnosed conditions such as Crohn’s disease or ulcerative colitis, there is no one size fits all method, and studies have shown that although diet can’t cure these conditions, it can help to calm your symptoms and allow you to lead a more comfortable lifestyle. 

Like many aspects of nutrition, knowledge is key, and this is particularly relevant to gut health in understanding how the gut affects our overall wellbeing. A nutrition professional can provide recommendations that are individualised to encourage a healthy, happy lifestyle.

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