Of course, Merino said, people with healthy diets may be different in many ways from those with less-healthful eating habits. So his team accounted for factors like age, race, exercise habits, smoking, body weight and whether people lived in low- or high-income neighborhoods.
Obesity, for example, is a risk factor for severe COVID-19. And body weight did explain a good portion of the connection between diet and COVID-19 risk, the study found.
But diet itself still showed a protective effect, the researchers noted.
The link was actually strongest among people who lived in economically deprived areas, Merino said. The researchers estimated that if one of those two factors was not present — poor diet or deprivation — almost one-third of COVID-19 cases in the study group could have been prevented.
Glatt cautioned, however, that it is very difficult to separate any effect of diet from everything else people do in their lives.
“There are just so many variables,” he said.
People who strive to eat healthfully, Glatt said, are probably careful about their health in general — and protecting themselves against COVID-19, specifically.
The researchers did ask respondents about their mask-wearing habits, and those responses did not explain the diet-COVID link.
But, Glatt said, “it’s impossible to account for everything” — including whether people worked from home, used public transportation, or were willing and able to avoid other crowded indoor situations.
Merino pointed to some other limitations of the study. While about one-quarter of respondents were age 65 or older, they were fairly healthy as a group — with few reporting chronic conditions like heart disease and diabetes.
Plus, Merino said, the survey was done in 2020 — before anyone was vaccinated and before the emergence of the highly contagious Delta variant.
Whether a healthful diet might have any additional impact in a vaccinated person, or during a time of Delta dominance, is unknown.
Those caveats made, both Merino and Glatt said that eating plenty of whole, plant-based foods is certainly a wise idea, since people with good nutrition are generally healthier and hardier.
“It’s quite reasonable to suggest that a healthy diet will be beneficial,” Glatt said.