A new study published in BMJ Prevention and Health has found that plant-based and pescatarian diets may help lower the odds of developing moderate to severe Covid-19 infection.

The study took place across six countries and found that a plant-based diet was associated with 73% lower odds of severe disease, while a pescatarian diet was associated with 59% lower odds of severe disease. 

Since the pandemic began, several studies have suggested that diet could play an important role in symptom severity and illness duration of Covid-19 infection. However, so far there has been little evidence to support this theory. 

To explore this further, the researchers drew on the survey responses of 2884 frontline doctors and nurses working in France, Germany, Italy, Spain, the UK and the US, all of whom had extensive exposure to SARS-CO-v2.

The researchers used the Survey Healthcare Globus network for healthcare market research to identify clinicians at high risk of Covid-19 infection from their jobs. The survey also gathered information on personal background, medical history, medication use, and lifestyle.

Those who ate a low carb-high protein diet nearly 4 times more likely to have moderate to severe Covid-19 infection

However, the main focus was to elicit detailed ​information about respondents’ dietary patterns, based on a 47-item food frequency questionnaire, and the severity of any Covid-19 infections they had had, using objective criteria.

​The various diets were then compiled into plant-based (higher in vegetables, legumes, and nuts, and lower in poultry and red and processed meats), pescatarian (the same as plant-based but with addition of seafood) and low carb-high protein diets.

In total, 568 respondents said they had had symptoms consistent with Covid-19 infection or no symptoms but a positive swab test for the infection. Of these cases, 138 clinicians said they had had moderate to severe COVID-19 infection, while 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. 

Those who ate a low carb-high protein diet had nearly 4 times the odds of moderate to severe Covid-19 infection compared with those who ate a plant-based diet. However, no association was observed between any type of diet and the risk of contracting Covid-19 infection or length of the subsequent illness.

Plant-based diets are thought to contribute to a healthy immune system 

The researchers note that the study is observational, so can't establish a cause. They also note than men outnumbered women in the study, so the results may not be applicable to women. 

However, plant-based diets are thought to contribute to a healthy immune system as they are rich in nutrients, especially phytochemicals (polyphenols, carotenoids), vitamins and minerals. Furthermore, fish is an important source of vitamin D and omega-3 fatty acids, both of which have anti-inflammatory properties. The properties of these foods could therefore help protect from poor outcomes from Covid-19. 

Deputy Chair of the NNEdPro Nutrition and COVID-19 Taskforce, Shane McAuliffe said: “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. 

“However, a high quality diet is important for mounting an adequate immune response, which in turn can influence susceptibility to infection and its severity.

"This study highlights the need for better designed prospective studies on the association between diet, nutritional status and Covid-19 outcomes."