Plant-based diet associated with lower risk of covid infection and less severe disease

In a recent study led by researchers at Massachusetts General Hospital (MGH) and Kings College Hospital published in Gut, people whose diets were based on healthy plant-based foods had lower risks of covid infection and severe disease.¹ The beneficial effects of diet on COVID-19 seemed especially relevant in individuals living in areas of high socioeconomic deprivation.

Poor metabolic health and unhealthy lifestyle behaviours have been associated with higher risk and severity of COVID-19 but evidence on the association of diet quality with susceptibility to and progression of COVID-19 was lacking.

The investigators examined data on 592,571 participants of the smartphone-based COVID-19 Symptom Study. Participants living in the U.K. and the U.S. were recruited from March 24, 2020 and followed until Dec. 2, 2020. At the start of the study, participants completed a questionnaire that asked about their dietary habits before the pandemic. Diet quality was assessed using a healthful Plant-Based Diet Score that emphasizes healthy plant foods such as fruits and vegetables.

During the study period, 31,831 participants developed COVID-19. Compared with individuals in the lowest quartile of the diet score, those in the highest quartile had a 9 percent lower risk of developing COVID-19 (HR 0.91; 95% CI 0.88 to 0.94) and a 41 percent lower risk of developing severe COVID-19 (HR 0.59; 95% CI 0.47 to 0.74). “These findings were consistent across a range of sensitivity analysis accounting for other healthy behaviours, social determinants of health and community virus transmission rates,” says lead author Jordi Merino.

The researchers also found a synergistic relationship between poor diet and increased socioeconomic deprivation with COVID-19 risk that was higher than the sum of the risk associated with each factor alone. Furthermore they estimated that nearly a third of COVID-19 cases would have been prevented if one of two exposures – diet or deprivation) – had not been present.

While the study supports the beneficial association of diet quality with COVID-19 risk and severity, particularly among individuals with higher deprivation, the authors acknowledge the possibility of residual confounding. People who eat healthier diets are likely to share other features that might be associated with lower risk of infection such as the adoption of other risk mitigation behaviours, better household conditions and hygiene, or access to care. Moreover, the study relied on self-reporting of dietary information which is prone to measurement error and bias.  In addition, as an observational study, the results do not confirm a direct causal association between diet and COVID-risk.

The investigators concluded that public health strategies that improve access to healthy foods and address social determinants of health may help to reduce the burden of the COVID-19 pandemic.

“Although we cannot emphasize enough the importance of getting vaccinated and wearing a mask in crowded indoor settings, our study suggests that individuals can also potentially reduce their risk of getting COVID-19 or having poor outcomes by paying attention to their diet,” says co-senior author Andrew Chan, a gastroenterologist and chief of the Clinical and Translational Epidemiology Unit at MGH.

Reference

1. Merino J, Joshi AD, Nguyen LH, et al. Diet quality and risk and severity of COVID-19: a prospective cohort study. Gut 2021;0:1–9. doi:10.1136/gutjnl-2021-325353