It’s been two years since COVID-19 first appeared in the United States, and scientists—and a weary public—are still debating the whys and wherefores of the pandemic.

While scientists and citizens argue over vaccines, treatments, masks, and social distancing, one fact is clear to all: COVID-19 isn’t going away. Given that ongoing reality, many of us remain determined to minimize our risk of catching COVID-19 and to minimize the severity of the disease if we get it. One tool is as close as your kitchen.

The role of metabolic health

Anyone with poor metabolic health has an elevated risk of disease. When metabolic processes, such as the absorption of nutrients and the regulation of blood sugar, are not working normally, your immune system is weakened, and it’s easier for microbes like viruses and bacteria to infect you. People with obesity, type 2 diabetes, heart disease, and cancer have impaired metabolism—and it’s scientifically established that they’re more likely to catch COVID-19 and to have severe or deadly disease. Data show that a 10 percent reduction in obesity, diabetes, and heart disease in the U.S. population would have prevented 11 percent of the hospitalizations from COVID-19 that have occurred since November 2020.

It’s also scientifically established that diet plays a role in metabolic illnesses like obesity, diabetes, and heart disease.

So an international team of 29 scientists and I conducted a study to answer this important question: Could the quality of a person’s diet affect the risk and severity of COVID-19—not just for people with poor metabolic health, but for everyone?

Our study

To answer that question, we used data from the smartphone-based COVID-19 Symptom Study, in which nearly 600,000 participants in the United States and the United Kingdom volunteered to provide information about COVID-19 symptoms and infections. The participants also provided information about their diet and lifestyle habits, including their consumption of plant-based foods (whole grains, fruits, vegetables, nuts and legumes) as well as processed or non-plant foods (potato chips, white bread, soda, sweets, fried eggs, and red meat).

The results, published in the medical journal Gut in October 2021, were interesting. We found that the people eating the healthiest foods were 9 percent less likely to get COVID-19 than those who ate the least healthy foods. If the healthy eaters did get the disease, they were 41 percent less likely to develop severe symptoms of COVID-19.

Diet didn’t have to be perfectly healthy to be protective. That is, protection didn’t come from eating only plant-based foods. Rather, small changes in diet—adding another serving of whole grains one day, or an additional serving of vegetables the next—was enough to generate a protective effect.

However, there was one confounding factor: People with “socioeconomic deprivation” who live in areas where healthy foods aren’t as affordable or available are more likely to get COVID-19 or suffer severe symptoms than people who don’t live in such areas. Yes, poor diet was a big contributor to excess risk for COVID-19, but so was deprivation.

All in all, if people ate a healthy diet and didn’t have socioeconomic deprivation, 33 percent of the cases of COVID-19 could have been prevented.

It’s also important to note that our observational study didn’t prove that a good diet was protective against COVID-19: It showed a possible association between a good diet and protection against the disease and its symptoms. But these results strongly suggest there may be a direct correlation between what you eat and how your body responds to the novel coronavirus.

More research

Researchers from Stanford University, Columbia University, Johns Hopkins University, and the Cedars-Sinai Medical Center also studied the link between diet and COVID-19, publishing their results in the June 2021 issue of BMJ Nutrition, Prevention, and Health. In a study of nearly 3,000 people from the United States and Europe, the researchers found that people who followed a plant-based diet had a 73 percent lower risk of moderate-to-severe COVID-19 than people who didn’t eat a plant-based diet.

They also found that people eating a pescatarian diet (plant-based foods plus fish and seafood) had a 59 percent lower risk. People who followed a “low-carbohydrate, high-protein diet” had a nearly four times higher risk of moderate-to-severe COVID-19.

Nutritional supplements

Nutritional supplements may also play a protective role. When researchers from King’s College London looked at health data from more than 400,000 women, they found that those who took a nutritional supplement were less likely to be infected with the coronavirus:

  • 14 percent less for those taking probiotics
  • 12 percent less for those taking omega-3 fatty acids
  • 13 percent less for those taking multivitamins
  • 9 percent less for those taking vitamin D.

Why a healthy diet is protective

Good nutrition and good immunity go hand in hand. There are many nutrients linked to stronger immunity:

  •  Trace elements: zinc, iron, and selenium
  •  Vitamins: A, B6, B12, C, D, and E
  •  Polyphenols, antioxidants found in plant foods.

Whole foods like vegetables, fruits, whole grains, and legumes are excellent sources of all these nutrients. Nutrients and nutritional compounds work in many ways to boost immunity—including supporting antiviral defenses that protect against a respiratory infection like COVID-19 and its severe symptoms.

While healthy diet and supplements can’t replace vaccines, masking, and social distancing, they can make those efforts more effective.

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