Vegans and pescatarians may be less likely to get severe Covid-19, a study suggests.

People whose diets are plant-based and those who eat fish but not meat appear to have lower odds of getting a severe infection compared with others.

Low-carbohydrate, high-protein diets appeared to be linked to an increased chance of getting moderate to severe illness, though the findings were not statistically significant.

The new study, published in BMJ Nutrition, Prevention and Health, examined data from healthcare workers across six countries including the UK.

Patients completed a web-based survey about whether they had Covid and their diets.

More than 2,300 did not have the disease and 568 did.

Among those who had Covid-19, 138 reported moderate to severe symptoms and 430 had mild or very mild illness.

Participant were asked to think about the diet they had in the year before Covid and were given  had 11 choices: whole foods, plant-based diet; keto diet; vegetarian diet; Mediterranean diet; pescatarian diet; Palaeolithic diet; low fat diet; low carbohydrate diet; high protein diet; other; none of the above.

Among the 568 participants who reported they had previously had Covid-19, 41 said they followed a plant-based diet.

And 46 said they followed a plant-based or pescatarian diet.

The authors estimated that participants who reported they had a plant-based diet were 73% less likely to report moderate to severe disease compared to those who did not follow one.

Pescatarians had 59% lower odds than people who followed other diets.

Compared with participants following plant-based diets, those with low-carb, high-protein diets were more likely to have moderate to severe Covid-19.

The authors, led by a team in the US, wrote: “In six countries, plant-based diets or pescatarian diets were associated with lower odds of moderate-to-severe Covid-19.

“These dietary patterns may be considered for protection against severe Covid-19.

“Plant-based diets or pescatarian diets are healthy dietary patterns, which may be considered for protection against severe Covid-19

Gunter Kuhnle, professor of nutrition and food science at the University of Reading, said: “Since the beginning of the pandemic, there has been a lot of speculation about the impact of diet on disease risk.

“This study attempts to answer this question, but there are a number of limitations that need to be considered: The study relied entirely on self-reporting, and a lot of data have shown that self-reported dietary intake is unreliable.

“In this study, participants were asked about their diet after they were diagnosed with Covid-19, and this might lead to further misreporting, especially among participants who are interested in a potential link between diet and disease.

“Finally, the study has been conducted in different countries with widely different diets – a plant-based diet in Spain or Italy is likely to be different from a mainly plant-based diet in Germany or the UK.”

Professor Francois Balloux of the UCL Genetics Institute said: “The study reports that doctors eating plant-based or pescatarian diets tend to be at significantly lower risk of developing severe Covid-19 symptoms upon infection.

“The sample size is decent, and the analyses look competently performed. Further validation may be required to confirm a direct, causal link between diet and Covid-19 illness severity.

“Indeed, unaccounted lifestyle variables correlated with diet might influence general health of the subjects of the study, and hence how well they coped with Covid-19 infection.”

According to the Eatwell guide, a vegan diet contains only plants such as vegetables, grains, nuts and fruits and foods made from plants. Vegans do not eat foods that come from animals, including dairy products and eggs.