RELATED: Can a Supplement Protect Me Against COVID-19?
Study Focused on Front-Line Workers With High COVID-19 Risk
Researchers analyzed survey responses from 2,884 doctors and nurses working in France, Germany, Italy, Spain, the United Kingdom, and the United States. Investigators sought out workers who had extensive exposure to SARS-CoV-2, the novel coronavirus responsible for COVID-19 infection, and excluded workers who were only infrequently exposed to patients with the virus. Nearly 95 percent of the participants were doctors, and 71.6 percent were male. The web-based survey, which was live from July to September 2020, included about 100 questions spanning the respondents’ medical history, current medications, lifestyle, COVID-19 symptoms, and food preferences. Researchers categorized respondents into one of three diet types based on their responses about how frequently they ate various foods: plant-based (high in vegetables, legumes, and nuts, and low in red and processed meats), pescatarian (a plant-based diet that includes seafood), and low-carbohydrate/high-protein. According to the survey, 568 participants reported either symptoms consistent with COVID-19 infection or no symptoms but a positive swab test for the infection. Of those 568 cases, 138 clinicians reported moderate to severe COVID-19 infection, which was defined as having a fever, respiratory symptoms, respiratory distress, or low oxygen saturation; the remaining 430 said they had had very mild to mild COVID-19 infection, characterized by no or very mild symptoms, a temperature below 100.4, and no shortness of breath or gasping. No one reported having critical COVID-19, which was defined by being in the ICU, having respiratory or other organ failure or needing a ventilator. RELATED: 10 Tips for Traveling Safely in the Time of COVID-19
People Who Ate More Fruits, Vegetables, and Fish Were Less Likely to Have Severe COVID-19
After analyzing the survey data, researchers found that respondents who followed a plant-based diet had a 73 percent lower risk of developing moderate to severe COVID-19; for those who followed a pescatarian diet, the risk was 59 percent lower. “We also found that those who followed low carbohydrate/high protein diets had greater odds of moderate to severe COVID-19 compared with those who followed a plant-based diet,” says Sara Seidelmann, MD, an internal medicine doctor at Stamford Health in Stamford, Connecticut, and a coauthor of the study. These associations remained even after factoring in body mass index (BMI) and coexisting medical conditions. Researchers controlled for several potentially influential variables, including age, ethnicity, medical specialty, smoking, and physical activity. Investigators didn’t find an association between any type of diet and the risk of contracting COVID-19 infection or the length of the subsequent illness. Although what you eat and drink can make a difference in preventing, fighting, and recovering from infections including COVID-19, no foods or dietary supplements can prevent or cure these diseases, according to the World Health Organization (WHO). To protect yourself from getting or spreading COVID-19, the Centers for Disease Control and Prevention (CDC) recommends getting a vaccine. If you aren’t fully vaccinated, wear a mask that covers your nose and mouth and stay at least six feet away from people outside your household. RELATED: How Obesity May Increase the Risk for COVID-19 Complications
Micronutrients Like Vitamins A, C, and E Are Linked to a Decreased Risk of Respiratory Infections
One potential explanation for the study results could be that fruits and vegetables have an abundance of micronutrients with immune-supporting properties. Plant-based diets are especially rich in compounds such as polyphenols and carotenoids, Dr. Seidelmann says. These plant chemicals support health in several ways, including stimulating the immune system and reducing the harmful cellular inflammation that is associated with infections. Individuals who follow plant-based diets tend to have a higher intake of vitamins A, C, and E, and minerals including iron, potassium and magnesium, as well as fiber, according to a study published in the Journal of Nutrition in November 2018. “In previous studies, supplementation of vitamins A, C, and E have decreased the risk of respiratory infections like the common cold and shortened the duration of these illnesses,” says Seidelmann. These nutrients support the immune system because they can help fight and destroy an invading virus or bacteria, she adds. A paper summarizing the role of nutrition, immunity, and COVID-19 published in May 2020 in BMJ Nutrition, Prevention & Health reported the benefits of vitamins A, C, and E for immune function and reducing host susceptibility to infection. Conversely, malnutrition and micronutrient deficiencies are associated with immune dysfunction, says Seidelmann. “Diets that are really rich in plants are generally less likely to be associated with micronutrient deficiencies,” she says. According to a review published in Nutrients in April 2020, micronutrient deficiencies negatively affect immune function and can decrease resistance to infections. RELATED: 9 Scientific Benefits of Following a Plant-Based Diet
Fats Found in Fish May Reduce Inflammation in People With COVID-19
While strictly plant-based diets were associated with the lowest risk of COVID-19 infection severity, the study results did indicate that pescatarians might also enjoy some of the same benefits. “Fish intake is an important source of vitamin D, as well as omega-3 fatty acids such as EPA and DHA,” says Seidelmann. Research is mixed on the impact of vitamin D in reducing the risk of COVID-19 infection or making the infection less severe, according to a paper published in the May 2021 Frontiers in Physiology. There is some evidence to indicate that people with a vitamin D deficiency may be more predisposed to getting the virus or progressing to more severe stages of the disease. Higher concentrations of EPA and DHA can reduce inflammation, according to the National Institutes of Health. A meta-analysis published in January 2019 in the Cochrane Database of Systematic Reviews found that people with acute respiratory distress syndrome who received formulas high in omega-3 fatty acids had shorter stays at intensive care units and needed mechanical ventilation for less time. RELATED: 7 of the Best Sources of Omega-3 Fatty Acids
The Fiber Found in Vegetables, Fruit, and Whole Grains May Support the Immune System by Improving the Gut Microbiome
Part of the benefit of the plant-based diet is not only what you are adding but what you may be subtracting, says Seidelmann. Some non-seafood proteins that come from animal sources, such as red or processed meats, are pro-inflammatory. People who get most of their protein from plant-based sources such as nuts, seeds, and whole grains are also reaping the benefits of a high-fiber diet, she says. Although this is a new area of research, there is evidence that fiber supports the microbiome, or network of healthy bacteria in your body. A robust microbiome plays a key role in immunity, says Seidelmann. “Fiber is sort of the substrate that these microbes grow and flourish off of. We don’t necessarily digest the fiber, but it is utilized in this way,” she says. Research on this is still in the early stages, but it appears that diversity and strains are present in plant-based diets that are not present in those people who follow a more meat-heavy Western dietary pattern, says Seidelmann. “The microbiome can influence your immune system,” says Elizabeth Bradley, MD, the medical director for the center for functional medicine at the Cleveland Clinic in Ohio. Dr. Bradley is part of a team currently examining the effects of a low-inflammatory diet on people who are COVID-19 long-haulers, a term used to describe those who have lingering symptoms of the disease, including fatigue, shortness of breath, brain fog, and trouble sleeping. High fiber, along with all the other nutritional advantages that a plant-based diet brings, can add more beneficial bacteria that would improve immune cell function, she says. Foods rich in fiber also provide vital nutrients like zinc, selenium, and other minerals that your body needs for improving your immune system through white blood cell function, says Bradley. “The fiber may play a role in multiple layers,” she adds. RELATED: 11 High-Fiber Foods to Add to Your Diet
More Research Is Needed to Strengthen the Association Between Diet and COVID-19 Severity
The study authors acknowledge a few limitations of their findings. The study was conducted very early in the pandemic, and people self-reported whether they followed a specific diet the past year, says Seidelmann. “Often people in nutritional studies don’t accurately recall what they have eaten, and they tend to overreport eating healthier food because they know they are being monitored,” says Bradley. Additionally, this was an observational study. “Care must be taken when you interpret the results of nutrition studies that are observational,” says Bradley. “This study showed a correlation with diet and COVID-19 severity, but it can’t establish cause.” Because observational studies don’t use a control, their results may be attributable to other factors. “People who eat healthier foods often have healthier lifestyles in lots of ways that could influence the results,” says Bradley. While future studies that address these issues and examine a wider segment of the population are needed, overall the findings are interesting and warrant further research, says Bradley. “In my mind,” she says, “these results are another endorsement for eating healthier.”
