The experience of Covid-19 varies widely among people. It can range from little to no symptoms at all to mild symptoms for a short period of time to full-blown life-threatening illness. The possible reasons for this enormous variation in disease process are still not clear. However, two new research studies are indicating that the difference may have a lot to do with the types of foods you are eating.
THE FIRST STUDY (1):
Results of one of the first studies to look at the effect of what you eat on the severity of Covid-19 disease were published in “BMJ Nutrition, Prevention and Health” in June 2021. The subjects of this research were 2,884 frontline doctors and nurses in France, Germany, Italy, Spain, the United Kingdom and the United States who reported a high frequency of exposure to Covid-19 patients. Their medical history, lifestyle, and frequency of eating certain foods was examined through a survey designed to pinpoint the association between dietary habits and the incidence, severity and duration of Covid-19 infection.
Out of all the participants, 2,316 of them did not experience Covid-19 symptoms or test positive for the virus. The remaining 568 individuals showed symptoms of Covid-19 or had a positive swab test. Of these subjects, 138 reported moderate-to-severe Covid-19 while the rest had mild to very mild cases.
The subjects of this study encompassed many different diet patterns. They were asked to choose the diet pattern that most resembled what they had been eating over the last year from among the following eleven diet types;
Whole foods, plant-based diet
Low fat diet
Low carbohydrate diet
High protein diet
None of the above.
Before any analysis was performed, diet types followed by at least 100 of the participants were selected and then the number of diet types for the purposes of this research was reduced to three by combining similar eating patterns.
1 The category, “plant-based diets”, included participants following “whole-food plant-based diets” and “vegetarian diets”.
2 To test if plant-based diets which include animal products might be associated with Covid-19 severity, a second category, “plant-based diets or pescatarian diets”, was created by combining “whole foods, plant-based diets”, “vegetarian diets” and “pescatarian diets”.
3 Finally, a “low carbohydrate, high protein diet” was created by combining “low carbohydrate diets” and “high protein diets”.
Results were as follows;
Those following “plant-based diets” lowered their risk of moderate-to-severe Covid-19 by 73% compared to those following other diets.
Those following “plant-based diets” or “pescatarian diets” lowered their risk of moderate-to-severe Covid-19 by 59% compared to those following other diets.
In comparison with those following “plant-based diets”, “low-carbohydrate, high-protein diet” eaters increased their risk of more severe Covid-19 disease by nearly four times.
The above associations remained after adjustments for confounding factors such as age, ethnicity, underlying medical conditions, level of physical activity, body weight, body mass index, smoking habits, or access to PPE (personal protective equipment).
Researchers credit the healthy nutrients in foods such as whole plants and fish for the resistance to Covid-19 that was observed in this study. Plant-based foods are rich in phytochemicals (such as polyphenols and carotenoids), fiber, vitamins and minerals while fish provide omega-3 fatty acids and vitamin D. Such nutrients support the immune system through their roles in the production of antibodies, the creation of lymphocytes (white blood cells that are an integral part of the immune system) and the reduction of oxidative stress. Diets high in plant materials are anti- inflammatory. Red and processed meats and processed foods are pro-inflammatory and linked to negative health outcomes. Worsening Covid-19 symptoms are associated with inflammatory factors.
Though this study identifies a correlation between the type of food being eaten and the severity of Covid-19, it does not establish causality. Future studies looking more deeply into macro-and micronutrient data will be necessary to elucidate cause.
THE SECOND STUDY (2):
Also released in June 2021 was a preprint of the results of another investigation into the association of diet quality with risk and severity of Covid-19. The study was launched by the health science company, Zoe, along with research colleagues at Harvard Medical School and King’s College in London. Its goal was to investigate the association of diet quality with risk and severity of COVID-19 and to look at how this effect intersects with socioeconomic deprivation.
Data was gathered from almost 600,000 participants. Diet quality was assessed through a healthful plant-based diet score emphasizing fruits, vegetables and whole grains, allowing oily fish, and limiting processed foods and refined carbohydrates.
This research discovered that those participants eating diets containing the most high-quality plant-based foods were associated with a 41% lower risk of contracting severe Covid-19 and a 9% reduction in falling ill with Covid-19 of any severity when compared to those participants eating diets lowest in high-quality plant-based foods. These results were particularly evident among persons living in areas of low socioeconomic conditions. The relationships remained after accounting for age, body mass index, ethnicity, smoking habits, mask-wearing habits, physical activity, underlying health conditions and population density.
This is the first study to show that a higher quality diet can reduce the chance of developing Covid-19 in the first place.
WHAT MIGHT THIS INFORMATION MEAN TO YOU?
Together these two studies point to the effects that your diet may be having, not only on contracting Covid-19, but also on the severity of the disease that will result if you do become infected. A healthier diet appears to significantly decrease the chances of contracting Covid-19 and, if you do come down with the disease, a high-quality diet can protect you from a more severe case. In addition, the second study showed that the association of a healthy diet with reduced Covid-19 risk is particularly evident in people living in poorer neighbourhoods. This is consistent with other current studies that demonstrate that people living in areas of greater social inequality are at approximately 25% higher risk of Covid-19 incidence and death when compared to those living under more affluent conditions and eating a diet of similar quality (3,4,5).
It remains unclear why diet might protect against Covid-19. However, inflammation may be at the heart of this matter. Diets low in quality foods are a known cause of inflammation and Covid-19 is a disease that produces a severe inflammatory response. Also, other recent research has shown that eating plants promotes a heathier and more diverse population of the microbes making up the microbiome and is associated with better overall health. This effect may also play a part (6).
The results of these studies bring to light yet another reason for making plant-sourced foods the stars of your dinner plate and relegating animal-sourced foods to a small corner or removing them altogether. Keep in mind also that choosing to eat a diverse variety of plants will mean that you are feeding and encouraging the growth of a wider variety of healthy microbes in your gut. It is becoming increasingly evident that a healthy gut microbiome leads to improved immunity and better overall health.
1 Kim, H., Rebholz, C.M., Hegde, S., et al. Plant-based diets, pescatarian diets and COVID-19 severity: a population-based case–control study in six countries. BMJ Nutr Prev Health. Published online June 7, 2021. Doi: 10.1136/bmjnph-2021-000272.
2 Merino, J., Joshi, A.D., Nguyen, L.H., Leeming, E.R, Mazidi, M. et al. Diet quality and risk and severity of Covid-19: a prospective cohort study. Preprint on MedRXiv; Doi: https://doi.org/10.1101/2021.06.24.21259283.
3 Wise, J. Covid-19: Highest death rates seen in countries with most overweight populations. BMJ 2021;372:n623. Doi:10.1136/bmj.n623.
4 Mena, G.E., Martinez, P.P., Mahmud, A.S., et al. Socioeconomic status determines COVID-19 incidence and related mortality in Santiago, Chile. Science 2021;372:eabg5298. Doi:10.1126/science.abg5298.
5 Feldman, J.M., Bassett, M.T. The relationship between neighborhood poverty and COVID-19 470 mortality within racial/ethnic groups (Cook County, Illinois). medRxiv 2020;2020.10.04.20206318. Doi:10.1101/2020.10.04.20206318.
6 Asnicar, F., Berry, S.E., Valdes, A.M. et al. Microbiome connections with host metabolism and habitual diet from 1,098 deeply phenotyped individuals. Nat Med 27, 321–332 (2021). https://doi.org/10.1038/s41591-020-01183-8.