Of course, said Merino, people with healthy diets can be different in many ways from those with less healthy eating habits. So his team took into account factors such as 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 explained much of the link between diet and the risk of COVID-19, according to the study.
But the diet itself has always shown a protective effect, the researchers noted.
The link was actually strongest among people who lived in economically disadvantaged areas, Merino said. Researchers estimated that if one of these two factors were not present – poor diet or deprivation – nearly a third of the COVID-19 cases in the study group could have been prevented.
Glatt cautioned, however, that it is very difficult to separate any effects of diet from everything people do in their lives.
“There are so many variables,” he said.
People who strive for healthy eating, Glatt said, are likely to take care of their health in general – and protect themselves against COVID-19, in particular.
Researchers asked respondents about their mask-wearing habits, and those responses did not explain the diet-COVID link.
But, said Glatt, “it’s impossible to explain everything” – including whether people worked from home, used public transportation, or were willing and able to avoid other crowded indoor situations.
Merino pointed out other limitations of the study. While about a quarter of respondents were 65 or older, they were quite healthy as a group – few reporting chronic health conditions like heart disease and diabetes.
Additionally, Merino said, the investigation was carried out in 2020 – before anyone was vaccinated and before the emergence of the highly contagious Delta variant.
It is not known whether a healthy diet could have an additional impact on a person vaccinated or during a period of Delta domination.
With these caveats, Merino and Glatt said that eating lots of whole, plant-based foods is definitely a good idea, as well-nourished people are generally healthier and more resilient.
“It’s entirely reasonable to suggest that a healthy diet will be beneficial,” said Glatt.