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  • Writer's pictureSophie Medlin

Covid and Gut Health: What Do We Know?

Did you know that some people still have COVID-19 detectable in their poo for months after they have been infected? Half of people still have COVID-19 detectable in their bowel in the week after diagnosis but 4% were still losing viral particles in their poo several months after catching the virus. These inactive viral particles are sometimes called ‘coronavirus ghosts’ and we think this may be part of the explanation for long-covid.

Lots of patients have been telling us that their gut symptoms have been much worse following a covid infection or that they have new symptoms after contracting covid. While this might not have been talked about much, it is certainly something that has been coming up clinically and there has actually been a lot of research into it.

Can COVID-19 cause gut symptoms?

The short answer to this is “yes”. As the virus has mutated and changed, we have seen more and more people with gut symptoms as a result of covid. For some people, these will go away, much like the respiratory aspect of the virus, but for others they may hang around and end up being part of a long-covid picture.

A study published in March 2022 showed that out of 147 patients with no prior gut issues, 16% reported having persistent gut symptoms around 100 days after they had been hosptialised with COVID-19. Within those who had symptoms, 7.5% had abdominal pain, 6.7% had constipation, 4.1% had diarrhoea and 4.1% had vomiting.

We have also seen that COVID-19 is affecting the gut-brain axis (how our gut and our brain communicate), with symptoms such as heartburn, swallowing problems, irritable bowel syndrome (IBS), boating, constipation and incontinence being reported.

How does COVID-19 affect the gut? (Get ready for the science bit)

There are several possible ways that COVID-19 causes gut symptoms but we’re not certain at this time which is the main cause.

What we do know is that the lining of the gut, much like our lungs and heart, has a large number of cells which are the known sites that the spike protein of COVID-19 attaches to in order to invade the body. These sites are called ACE-2 receptors and within the gut, we have the largest number of them in the small bowel but they are also present in the colon, stomach, oesophagus, liver, biliary tract and pancreas. This means that there are many places in the bowel that COVID-19 can enter the body.

In a healthy gut, ACE-2 has a number of really important roles including helping to regulate blood flow within the gut, protecting the permeability of bowel wall (keeping some things in and other things out) and optimising muscle contraction which helps with the flow of poo matter through the bowel. They are also involved in preventing inflammatory processes. When the spike protein of COVID-19 attaches to the ACE-2 receptors and invades the cells, they are unable to carry out their normal functions.

Once the virus has entered the intestinal cell walls via the ACE-2 receptors, it can destroy the tight junctions between the cells on the lining of the gut. These vital physical barriers prevent bad bacteria entering our body. Without these working properly, bad bacteria may enter circulation and cause systemic inflammation and infection. It is thought that this contributes to the ‘cytokine storm’ seen in severe COVID-19 infections.

It is plausible therefore that when COVID-19 has flooded the gut, ACE-2 receptors aren’t able to carry out their normal functions which can affect, blood flow, the function of the gut lining, the movement or motility within the gut and potentially cause inflammation of the nerves, affecting the gut-brain axis.

What is the role of the microbiome?

In mouse studies, rodents without a healthy microbiome produce far more ACE-2 expression across the bowel than those with a healthy microbiome. This gives more sites for COVID-19 to attach to which may increase the level of infection within the gut and how long the symptoms last for.

COVID-19 infection disrupts gut bacteria by decreasing the proportions of probiotic (good) bacteria and increasing the numbers of pathogenic (bad) bacteria. This may contribute to the bowel symptoms people are experiencing post COVID-19 infection as COVID will have reduced their numbers of good bacteria.

We also know that people who take anti-acid medication (PPIs), often had worse outcomes from COVID-19. This is thought to be due to the negative impact of PPIs on our gut bacteria.

It is likely that having a healthy microbiome (gut bacteria) may offer a better physical barrier throughout the gut, making it harder for the COVID-19 virus to find and adhere to ACE-2 receptors.

We also think that the short chain fatty acids produced by beneficial bacteria within the gut and the respiratory tract are highly protective against a severe COVID-19 infection. They are shown to promote anti-COVID-19 antibody production and therefore prevent the development of a COVID-19 infection at a cellular level. Short chain fatty acids from bacteria also have a strong anti-inflammatory effect which is thought to protect from the ‘cytokine storm’.

It may seem obvious, given the information above to say that people with low microbial diversity or a poor microbiome are more likely to have worse outcomes if they do come into contact with COVID-19 and this is a very reasonable hypothesis but we don’t have definitive proof of this as yet.

Researchers are looking at the potential benefits of pro and prebiotics in the prevention of severe COVID-19 but there isn’t any clear evidence to show what the best strains would be at the moment.

How can you treat COVID-19 in the Gut?

To date, we don’t have any definitive answers to how we can reverse the gut symptoms from COVID-19. Working theories include the use of pro and pre-biotics to restore the healthy microbiome we require to dampen down inflammation and support healthy digestion.

Eating a well-balanced diet with plenty of plant fibre will help to support your microbiome in getting back to health and will also provide your body with lots of vitamins and antioxidants which are important for recovery after any infection.

It is known that glutamine, which is an amino acid, is essential for a healthy gut lining which may be compromised in COVID-19 infections. Under physiological stress - such as fighting a virus - our glutamine requirements increase significantly. Some people hypothesise that supplementation with glutamine may help restore the integrity of the gut lining following COVID-19 infection.

Reducing fermented carbohydrates (FODMAPS) may help to reduce symptoms in those who have ongoing gut problems after catching COVID-19. This should always be done under the supervision of a dietitian as it may cause longer-term damage to the gut microbiome if it’s not done correctly.

In the case of diarrhoea and constipation, alongside restoring the microbiome through your diet and potentially supplements, using over-the-counter anti-diarrhoeal or laxative medication may be appropriate. As always, ongoing symptoms need to be seen by your doctor and referral to a dietitian via the NHS or a self-referral to private clinics is advised.


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