The study of 2884 frontline doctors and nurses with extensive exposure to SARS-CO-v2 indicates that those following plant based and pescatarian diets were 73% and 59% less likely to suffer moderate-to-severe illness, respectively.
The researchers drew on the survey responses of healthcare professionals from France, Germany, Italy, Spain, the UK and the US, registered with the Survey Healthcare Globus network for healthcare market research.
The online survey, which ran between July and September 2020, was designed to elicit detailed information about respondents’ dietary patterns, based on a 47-item food frequency questionnaire, over the previous year, and the severity of any COVID-19 infections they had had, using objective criteria.
The survey also gathered information on personal background, medical history, medication use, and lifestyle.
The various diets were combined into plant-based (higher in vegetables, legumes, and nuts, and lower in poultry and red and processed meats); pescatarian/plant-based (as above, but with added fish/seafood); and low carb-high protein diets.
Some 568 respondents (cases) said they had had symptoms consistent with COVID-19 infection or no symptoms but a positive swab test for the infection; 2316 said they hadn’t had any symptoms or tested positive (comparison group).
Among the 568 cases, 138 clinicians said they had had moderate to severe COVID-19 infection; the remaining 430 said they had had very mild to mild COVID-19 infection.
After factoring in several potentially influential variables, including age, ethnicity, medical specialty, and lifestyle (smoking, physical activity), respondents who said they ate plant-based diets’ or plant-based/pescatarian diets had, respectively, 73% and 59% lower odds of moderate to severe COVID-19 infection, compared with those who didn’t have these dietary patterns.
And compared with those who said they ate a plant-based diet, those who said they ate a low carb-high protein diet had nearly four times the odds of moderate to severe COVID-19 infection.
These associations held true when weight (BMI) and co-existing medical conditions were also factored in.
But no association was observed between any type of diet and the risk of contracting COVID-19 infection or length of the subsequent illness.
The researchers note this is an observational study, and so can’t establish cause, only correlation. It also relied on individual recall rather than on objective assessments, and the definition of certain dietary patterns may vary by country.
But plant-based diets are rich in nutrients, especially phytochemicals (polyphenols, carotenoids), with prior studies reporting higher fibre, vitamins A, C, and E, folate, and mineral (iron, potassium, magnesium) intake among those with highest versus lowest adherence to plant-based diets.
Studies have reported that supplementation of some of these nutrients, specifically, vitamins A, C, D, and E, decreased the risk of respiratory infections, such as the common cold and pneumonia, and shortened the duration of these illnesses. These nutrients are hypothesised to support the immune system as they play important roles in the production of antibodies, proliferation of lymphocytes, and reduction of oxidative stress.
Fish intake is an important source of vitamin D and omega-3 fatty acids EPA and DHA. High EPA and DHA intake, which results in the formation of omega-3 oxylipins, have anti-inflammatory effects, suppressing the production of pro-inflammatory cytokines (interleukin 1β, tumour necrosis factor α), reducing inflammatory eicosanoid synthesis and oxidative stress.
A meta-analysis of 10 randomised controlled trials in patients with acute respiratory distress syndrome (ARDS) found that individuals who received formulas high in omega-3 fatty acid had shorter duration of mechanical ventilation and shorter length of stay at intensive care units.
“Our results suggest that a healthy diet rich in nutrient dense foods may be considered for protection against severe COVID-19,” they conclude.
“The trends in this study are limited by study size (small numbers with a confirmed positive test) and design (self-reporting on diet and symptoms) so caution is needed in the interpretation of the findings,” comments Deputy Chair of the NNEdPro Nutrition and COVID-19 Taskforce, Shane McAuliffe.
“However, a high quality diet is important for mounting an adequate immune response, which in turn can influence susceptibility to infection and its severity."
He adds: “This study highlights the need for better designed prospective studies on the association between diet, nutritional status and COVID-19 outcomes."
Source: BMJ Nutrition Prevention & Health
Kim H, Rebholz CM, Hegde S, et al
"Plant-based diets, pescatarian diets and COVID-19 severity: a population-based case–control study in six countries"