A healthy gut helps keep your immune system strong. Plus, new research continues to link gut health with COVID-19 severity and symptoms. We sat down with Will Bulsiewicz, M.D. to get the scoop on the latest gut-health research and what to eat to keep your gut strong and healthy.

Lisa Valente, M.S., RD
January 21, 2021
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Gut health is a hot topic. The trillions of bugs that live in our digestive tract impact our health in myriad ways. A healthy gut is linked to better moods and less stress, and can affect our weight, heart health and more (here are three surprising reasons your gut health matters). In the midst of the coronavirus pandemic, many of us have been wondering if what we eat can help keep us healthy. There's been research around vitamin D and COVID-19, what foods can help boost your immunity, and if gut health plays a role in the severity of COVID-19 symptoms.

Last week, new research, published in Gut, had us looking more closely at the importance of a healthy gut in the midst of the pandemic. We talked with Will Bulsiewicz, M.D., author of Fiber Fueled: The Plant-Based Gut Health Program for Losing Weight, Restoring Your Health, and Optimizing Your Microbiome to talk about the latest study, what we should be eating and avoiding for a happier gut microbiome and how to take care of ourselves during the coronavirus pandemic. (Responses have been edited for length and clarity.)

Can you explain what the latest research shows about coronavirus and gut health? 

There was a new paper that came out last week, published in Gut. The general point of the study was that the inflammation that starts with your gut microbes may be what is determining who gets mild versus severe COVID-19. The study showed that unique changes to the gut microbes were consistently found across people who had COVID-19, compared to those who did not. The more severe that your COVID-19 symptoms were correlated to changes in the microbiome [think: the person in the ICU versus mild symptoms]. As severity gets worse, this microbiome profile gets more solidified. What they found was that people with severe COVID-19 had higher levels of inflammatory markers, correlating to these changes in the microbes.

We know that in people with severe manifestation of COVID-19, a big problem is inflammation. It's not the virus, but the effects the virus has on our body and how our body reacts to it. We've been trying to understand why some people barely even know they have COVID-19 and some people are exposed to the same virus and get intensely sick in the ICU. We've been trying to find answers, and the study suggests the answer may lie in our gut microbes. 

The specific pattern that they noticed was that if you developed COVID-19 you had more microbes that produce inflammation and there was a loss of specific microbes that are known to be anti-inflammatory. If you zoom in on this and find the missing microbes, these are the microbes that are known to produce butyrate. Butyrate is the product of short-chain fatty acids, and is produced when we consume fiber. It's incredibly anti-inflammatory. 

It was an association study, so we can't say definitively that it was the gut microbes affecting the disease or that the gut microbes are a product of the disease. We do know that these microbes are very well defined, and that the missing ones are anti-inflammatory and the ones that are present are inflammatory, and we see it correlating to markers of inflammation.

What have we learned so far about gut health and COVID-19?

It was my suspicion months ago that gut health was going to play a role. Older studies, not with COVID, but with other respiratory viruses, have looked at what's happening in the microbiome. In one animal-model study (so take it with a grain of salt, but we can dig into mechanisms), [researchers] were very, very surprised when they discovered that a high-fiber diet allowed mice to live longer with less severe respiratory symptoms and better lung function. They were surprised because they thought you needed inflammation to clear out the infection and they knew the high-fiber diet was anti-inflammatory.

They found that the fiber was working through the gut microbiome to produce butyrate and butyrate was selectively altering the immune system by turning it up to fight the virus, and turning it down in other spots to avoid excessive inflammation. It was targeting the virus without an excessive immune response in these mice. These mechanisms demonstrate that a high-fiber diet can give our immune system an edge through the microbiome. Combine this with the new study in humans suggesting that the microbiome is a piece of what's missing in fighting this virus.

What foods should people be eating for gut health during the pandemic? 

The answer is simple. Our microbes' favorite food is fiber. You find fiber in all plants. Fruits, vegetables, whole grains, seeds, nuts and legumes all contain fiber. What we've discovered is that different plants contain different types of fiber. Microbes are picky eaters. Fiber is not just a generic thing. Some microbes like beans, some like farro or quinoa, some like apples. The best way to optimize the gut microbiome is to eat a wide variety of plants, as many different plants as possible.

A plant-based diet, with variety, is the optimal diet for gut health. (Learn more about what foods to eat on a plant-based diet and how to get started.)

What foods should people be avoiding for gut health during the pandemic? 

After antibiotics, the next thing that destroys the microbiome is alcohol. Many people are reaching for more wine and more beer during this pandemic for myriad reasons. The other thing to be conscious of is highly processed foods: whether it's processed meat or sweets or even processed plant foods, these foods are clearly causing damage to the microbiome. We want to move away from processed foods, which make up 60% of Americans' diets right now, and only 10% or less is coming from real plants. We need to flip that. We should be 60% plant-based and 10% or less in terms of processed foods. 

I'm of the belief that the healthiest amount of alcohol is none. But, full disclosure, I have a glass of wine once in a while. The key is to not make a habit of drinking. Having a date night and having a glass of wine is OK once in a while.

What about gut-health supplements?

You can't take a C-minus gut and turn it into an A-plus with supplements of any variety. Supplements aren't enough to overcome an unhealthy diet and lifestyle. Make sure you're getting a good night's rest, exercising, having a strong stress-relief practice. All those things are relevant to gut health, and there are ways to improve gut health without picking up a fork. Do I believe in prebiotics? Yes. Do I believe in probiotics? Sometimes. Prebiotics are food for your microbiome. If they're not being fed, [the microbes] starve and they're weak and can't do anything. Prebiotic fiber is one way to support a healthy gut. But we want most of our fiber to come from real food, not supplements. (Learn more about prebiotics and foods they're in). 

We all have to eat and we all want convenience. You'll see "prebiotics" and "probiotics" and "plant-based" in processed foods, but stick to whole foods most often. 

Is there anything in particular we should be doing during the pandemic for gut health? 

The pandemic is motivation to double down on healthy practices. I'm by no means perfect. But I know how important a healthy gut is. I've been using the pandemic as motivation to follow the recommendations and rules in my book Fiber Fueled. I wrote the book to show people how they can enhance their gut health. 

Health and wellness does not need to be difficult. We just need to stop searching for shortcuts and embrace what we know is true. We all know we should be eating more fruits and vegetables. It's so simple. We need to create lifestyle habits that allow us to do that while acknowledging the pressures of 21st-century life. There's a reason people reach for convenience foods—they have stress in their life—so it's a matter of creating healthy habits. I'm a big believer in progress over perfection. Let's not shoot so high that we are incapable of accomplishing our goals. Let's make realistic goals and achieve them.