If you want to lessen your chance of developing severe coronavirus symptoms, a new paper has suggested that vegan, vegetarian and pescetarian diets are the way to go. But does it really make that much of a difference?
According to the BMJ, your odds of developing moderate to severe COVID-19 could be lowered 73% by a plant-based diet or 59% by fish-based diets. These statistics are based on a recent study carried out across six countries.
Protecting against COVID-19 through certain diets and foods is something which has been suggested since the beginning of the pandemic. The reliability of these claims can sometimes be difficult to gauge.
Gathering results from the US, France, Germany, Italy, Spain and the UK, researchers for the most recent study drew on survey responses from 2884 frontline doctors and nurses with extensive exposure to SARS-CO-v2, the virus responsible for COVID-19 infection. Lifestyle information was also gathered by the survey including personal background, medical history and medication use.
A network for healthcare market research, the Survey Healthcare Globus network, allowed the researchers to connect with these participants through a global network of healthcare professionals. In selecting participants, researchers prioritised clinicians whose jobs placed them at high risk of COVID-19 infection. Using objective criteria, the online survey ran between July and September 2020 and was designed to elicit detailed information about respondents’ dietary patterns over the past year (based on a 47-item food frequency questionnaire) and the severity of any COVID-19 infections they had had. Of those surveyed, 2316 said they had not tested positive or had any symptoms, while 568 said they had had a positive swab test for infection and/or symptoms consistent with COVID-19 infection. A mild or very mild COVID-19 infection was reported by 430 of the positive cases, while the remaining 138 clinicians said they had had moderate to severe COVID-19 infections.
To allow comparison, the various diets reported were grouped into low carb/high protein diets, plant-based (low in poultry and red and processed meats and high in nuts, vegetables and legumes) and pescatarian/plant-based (as above, but with added seafood or fish).
Risk of contracting moderate-to-severe COVID-19 additionally appeared to be increased in those who reported eating a low-carbohydrate or high-protein diet. Researchers found that factoring in BMI and co-existing medical conditions did not alter these results. The odds of a moderate to severe COVID-19 infection was nearly four times higher in those who ate a low carb/high protein diet, compared with those who said they ate a plant-based diet.
All of these results make a strong case for the idea that you can reduce or increase your risk of COVID-19 through certain food choices – such as being a fish eater or vegetarian. But things are rarely so simple.
Barriers to Accuracy: Small Samples and Self-Reporting
One point worth noting is that respondents’ initial risk of contracting COVID-19 did not appear to be influenced by their reported diet type. Your risk of getting infected, according to this study, is not affected by your diet. The length of illness also did not appear to be impacted. The only thing the study discusses is a potential link between diet and severity of symptoms. Only correlation could be established by this observational study – no causes.
The researchers have also pointed out that the study relied on individual recall rather than objective assessments, and that the definition of certain dietary patterns may vary country by country. They note, however, that plant-based diets are rich in nutrients, especially phytochemicals (carotenoids and polyphenols), vitamins and minerals, all of which are important for a healthy immune system. They conclude that their results “suggest that a healthy diet rich in nutrient dense foods may be considered for protection against severe COVID-19”.
Researchers add that fish is an important source of vitamin D and omega-3 fatty acids, both of which have anti-inflammatory properties.
The number of people involved should also be considered here. Only 138 health professionals who had developed moderate-to-severe disease took part, with just under 3,000 overall respondents across six western countries. Each participant had to select one diet out of 11 options, dividing the sample number into smaller groups, and the small number of serious positive cases into smaller groups still.
The researchers add that men outnumbered women in the study, meaning the findings may not be applicable to women.
In order to produce meaningful results, the small groups meant that fish eaters had to be lumped in with vegetarians and vegans. Only five fish-eaters got COVID-19 in the end, and just 41 vegans/vegetarians contracted the disease. Of these 46 cases, only a few went on to develop severe symptoms. Statisticians call this type of problem a type 1 error: working with small numbers and consequently increasing the risk of falsely identifying a relationship between factors that doesn’t exist.
Shaun McAuliffe, Deputy Chair of the NNEdPro Nutrition and COVID-19 Taskforce, has said that “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.”
As mentioned above, observational studies like this can’t pin down any causality between diet and COVID-19 symptoms. Running the test as an intervention instead would show causality – i.e. getting someone to switch to the diet for the purpose of the study, allowing a set amount of time for the change to have an effect, and then comparing the case to a control group.
So what should our takeaway be? Since no studies have proven that you can avoid COVID-19 through diet alone, the best course of action is to continue following the public health advice of vaccinations, masks and distance. That said, you will never regret making your diet a little healthier, so if you choose to try and reduce your risk by eating more vegetables and fish on top of getting vaccinated, it can only be a good thing. If you want to learn more about the types of foods you can eat to improve your health, check out our Essential Guide to Food for Health.
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