TUESDAY, Sept. 14, 2021 (HealthDay News) -- People who eat plenty of fruits and vegetables may have a somewhat lower risk of COVID-19 than those with unhealthy diets, a new study suggests.
Of more than 590,000 adults surveyed, researchers found that the quarter with the most plant-rich diets had a 9% lower risk of developing COVID-19 than the quarter with the least-healthy diets.
Their risk of severe COVID-19, meanwhile, was 41% lower, according to findings recently published online in the journal Gut.
Experts were quick to stress that healthy eating is no magic immune-booster that will ward off COVID-19.
"This doesn't change anything. Get vaccinated," said Dr. Aaron Glatt, an infectious disease specialist and spokesman for the Infectious Diseases Society of America.
Jordi Merino, the lead researcher on the study, agreed that no one should consider diet a replacement for vaccination or other measures, like wearing a mask.
Instead, the findings suggest that poor diet quality may be one of the social and economic contributors to COVID-19 risk.
So making healthy foods more accessible to low-income Americans could be one way to help ease the burden of the pandemic, according to Merino, a researcher at Massachusetts General Hospital in Boston.
The findings are based on over 592,000 U.S. and British adults who were part of a smartphone survey. They reported on any COVID-19 symptoms they developed and whether they'd tested positive for the disease. They also completed a diet questionnaire asking about their intake of various foods during a typical week.
Merino's team divided participants into four groups based on their intake of plant foods like fruits and vegetables, whole grains, legumes and vegetable oils.
During the study period, there were 31,815 documented cases of COVID-19.
On average, the researchers found, the one-quarter of participants with the most plant-rich diets were slightly less likely to develop COVID-19 than the quarter with diets devoid of fruits and vegetables.
And when they did get sick, their risk of severe COVID (requiring hospitalization and oxygen) was 41% lower. In absolute terms, the rate of severe COVID-19 was 1.6 per 10,000 people per month in the group with the healthiest diets; in the group with the poorest diets, the rate was 2.1 per 10,000 each month.
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.
The World Health Organization has more on COVID-19 and nutrition.
SOURCES: Jordi Merino, PhD, research associate, Diabetes Unit and Center for Genomic Medicine, Massachusetts General Hospital, and instructor, medicine, Harvard Medical School, Boston; Aaron Glatt, MD, chief, infectious diseases, Mount Sinai South Nassau, Oceanside, N.Y., and spokesman, Infectious Diseases Society of America, Arlington, Va.; Gut, Sept. 6, 2021, online