TORONTO -- Poor gut health could put you at risk of more severe outcomes if you have COVID-19, according to a new scientific review.
The review, published this week in mBio, found that those who had more serious cases of COVID-19 tended to also have gastrointestinal symptoms. It theorizes that an altered gut microbiome could allow COVID-19 to spread to more organs faster, and could be an underlying factor in known risk factors such as chronic disease.
The most common symptoms associated with COVID-19 are high fevers and respiratory issues, but the virus can attack other parts of the body, including the gastrointestinal system. When COVID-19 patients become sick enough to require hospitalization, the review observed that a large percentage of these patients also experience diarrhea, nausea and vomiting as part of their symptoms.
The review suggests that if the virus is able to enter the gastrointestinal system, it worsens the patient's outcome -- and having an altered gut microbiome makes it easier for the virus to find its way into that system.
Microbiologist Heenam Stanley Kim, from Korea University's Laboratory for Human-Microbial Interactions, sifted through numerous studies in order to paint a bigger picture of the accumulating evidence for the theory.
"There seems to be a clear connection between the altered gut microbiome and severe COVID-19," Kim said in a press release.
Poor gut health is associated with "leaky gut," a term that refers to an unhealthy gut lining that has cracks that allow bacteria, toxins or partially digested food to leak through into the bloodstream.
While the intestinal lining always has some level of permeability, usually it tightly controls what is absorbed into the bloodstream. If this process is disrupted by an unhealthy lining, it could result in inflammation and changes to the regular bacteria in the gut.
And in COVID-19 patients, a leaky gut could mean much worse outcomes from the virus, Kim believes.
Leaky gut could allow the novel coronavirus to more easily access "the surface of the digestive tract and internal organs." If the novel coronavirus could penetrate through the gut barrier into the bloodstream, it could potentially spread quickly to other organs.
"These organs are vulnerable to infection because they have widespread ACE2--a protein target of SARS-CoV-2--on the surface," the release stated.
It has been well-established that COVID-19 largely attacks the respiratory system. But post-mortems done on those who have died of COVID-19 have found viral loads in multiple organs, including the heart, liver, brain and kidneys, suggesting that severe outcomes may be more likely when the virus spreads to more organs -- something that needs more research, the review noted.
Some of the most well-known risk factors for COVID-19 -- advanced age and chronic conditions such as diabetes -- are also connected to "altered gut microbia," the review pointed out.
While the review suggests that poor gut health could be associated with more severe COVID-19 cases, it also notes that this theory hasn't been empirically proven yet. Further research is needed to show a direct link between patients with severe cases of COVID-19, gut symptoms like diarrhea and a leaky gut.
The studies Kim analyzed showed that there was a "complicated relationship," between gut health and COVID-19, the release stated.
For instance, COVID-19 has been associated with a depletion in the variation of bacteria in gut samples taken from COVID-19 patients, in comparison with samples from healthy people. The specific bacterial species that were reduced include some that produce a short-chain fatty acid that aids with strengthening the gut barrier.
Poor gut health is something that still isn't fully understood by doctors and scientists. But research has shown that poor eating habits can change the gut flora. Kim decided to look at studies that examined the connection between gut health and COVID-19 because he noticed that the virus was spreading particularly intensely in many Western countries, where many have a diet low in fiber.
"A fiber-deficient diet is one of the main causes of altered gut microbiomes," he said in the release. "And such gut microbiome dysbiosis leads to chronic diseases."
If a stronger connection between gut health and severe cases of COVID-19 is proven in further research, Kim says it could potentially open up new opportunities for disease prevention or strategies to lower the chance of severe outcomes, from medical treatments to dietary changes.
"Simply increasing the daily intake of dietary fiber may markedly help improve gut health," the review theorized. "This dietary adaptation may be the most easy and effective method that can be considered to be implemented immediately to prevent severe COVID-19 or just for general health improvement."
