The Gut Health Advantage: How Fiber May Reduce Risk for Long COVID
As new studies reveal a link between gastrointestinal problems (such as indigestion and irritable bowel syndrome) and Long COVID, researchers are posing the question: Are there any nutritional interventions that could help patients?
Early research suggests that our gut health is closely linked to Long COVID. Reduced biodiversity of our microbiomes, the community of “good” and “bad” bacteria that resides in our gut, may increase risk for Long COVID, one recent study reported. “Good” bacteria, associated with a more diverse microbiome, help to break down food into energy sources for our bodies to use and also seem to play a role in aiding our immune systems. “Bad” bacteria can take over in situations where our microbiome diversity is reduced (often due to an unhealthy diet) and tend to not do as good a job at converting our food to useful energy sources for our bodies.
In another study, researchers using machine learning accurately linked gastrointestinal symptoms of Long COVID (upper abdominal pain, bloating, etc.) to a patient’s microbiome in 89% of cases. Taken together, the evidence seems to suggest that reduced microbiome diversity and the proliferation of “bad” bacteria may be connected to a higher prevalence of Long COVID symptoms. These studies do not definitively explain why we have gastrointestinal symptoms with Long COVID. However, they provide plausible hypotheses and empirical evidence that can lay the foundation for formulating strategies to tackle these nagging Long COVID gut issues.
Fermentable fiber for Long COVID?
This connection between our gut and Long COVID has led researchers at Monash University in Melbourne, Australia, to study fermentable fiber—found mainly in foods rich in a type of dietary fiber known as soluble fiber—and its role in alleviating Long COVID symptoms, such as gastrointestinal distress. Fermentable fiber, which is naturally found in legumes, fruits, vegetables, and whole grain breads and cereals, aids in digestion, helps to improve microbiome diversity, and may also support our immune systems in the fight against Long COVID. Jane Varney, PhD, senior research dietitian in the department of gastroenterology at Monash University and one of the investigators of the fermentable fiber study, provides a more extensive list of fiber sources here.
“[Fermentable fiber] is a top fiber in food that has a whole range of health benefits—one of which might be to improve immune function,” says Varney. “Fermentable fibers are converted by gut bacteria to metabolites such as short chain fatty acids (SCFAs). These metabolites, in turn, reduce inflammation and improve immune function.”
A simple, but effective study design
In their ongoing study, the research team is giving one group of patients a supplement containing inulin (a form of fermentable fiber found in various fruits and vegetables) and another group rice flour (a low-fiber form of starch used in cooking) to act as a control. The researchers will assess whether the inulin improves the gut microbiota measured through stool studies by improving microbiome diversity. Follow-up studies will then investigate whether this microbiome boost has a positive impact on Long COVID symptoms. If the results are positive, the researchers hope to conduct a larger trial.
However, the researchers note that it’s not yet known whether byproducts from these fibers will irritate the digestive systems of certain people—especially those with conditions such as irritable bowel syndrome, which can lead to sensitive bowel walls. Therefore, the team will be closely monitoring how the study participants respond to the fiber.
“A lot of evidence in mouse models supports [the use of] fermentable fiber, but the doses are beyond what is realistic for a person to eat,” says Paul Gill, PhD, research fellow at Monash and study co-investigator. “Fermentable fibers won't be a practical solution if there are side effects such as bloating.”
Bubu Banini, MD, PhD, assistant professor of medicine (digestive diseases) at Yale School of Medicine, who is not involved in the study, is optimistic about the research. She believes that the study has a simple design that will answer an important question. “If the study shows fermentable fibers are effective [at reducing risk for Long COVID], that would be a win since fiber is cheap and readily available,” she says. “Repurposing agents that are already available are attractive due to affordability and accessibility. New meds don’t typically have those characteristics.”
As Gill writes in his blog, Long COVID is a challenging disease with limited treatment options. Nevertheless, research into our microbiomes—and how supplements like fermentable fiber can improve them—will continue to shape how we view Long COVID and the strategies clinicians pursue to treat it.
Fermentable fibers show promise as a supplement to not only treat Long COVID, but also to act as a preventative measure for patients predisposed to gastrointestinal issues. However, more work needs to be done to verify its effectiveness.
If you are experiencing any chronic symptoms, such as digestive issues, after a previous bout of COVID-19, reach out to your primary care physician for guidance.
Fabrizio Darby is an MD candidate at Yale School of Medicine.
The last word from Lisa Sanders, MD:
Fiber is a key ingredient of a healthy diet. Diets that are high in fiber are associated with a broad spectrum of health benefits, including improved metabolism and heart health. However, most of us don’t get the fiber we need.
There are two types of dietary fiber. Soluble fibers mix with water in the GI tract and slow digestion. They are associated with a decreased risk of heart disease, lower cholesterol levels, and better blood sugar control. Soluble fiber can be found in some grains, seeds, legumes, and various vegetables as well as in some supplements, such as Metamucil in the form of psyllium husk. This type of fiber is most easily tolerated in patients with irritable bowel syndrome (IBS).
Insoluble fibers are found in foods such as whole grains, beans, and root vegetables. They act as bulk that can help food and waste pass through the gut more quickly and easily. But insoluble fibers act, in part, by stimulating the lining of the GI tract and in some can cause irritation, bloating, and gas.
Many of the GI symptoms of Long COVID mimic those of IBS, so it’s not surprising to me that the addition of soluble fiber could be helpful. Psyllium, the primary ingredient in Metamucil and other soluble fiber supplements, has been widely tested in those with IBS and shown to help with bloating and pain, as well as reduce both constipation and diarrhea. If you decide to give soluble fibers a go, remember to start slowly and increase to the recommended dose carefully. Our GI system does not like sudden movements. If you use a psyllium-containing product like Metamucil, remember to take it with PLENTY of water. A full 8-ounce glass of water is probably enough; two wouldn’t hurt.
Read other installments of Long COVID Dispatches here.
If you’d like to share your experience with Long COVID for possible use in this blog (under a pseudonym), write to us at: LongCovidDispatches@yale.edu. It may appear, space permitting, in a future post.
Information provided in Yale Medicine content is for general informational purposes only. It should never be used as a substitute for medical advice from your doctor or other qualified clinician. Always seek the individual advice of your health care provider for any questions you have regarding a medical condition.
