Plant-based and/or fish diets may help lower the odds of developing moderate to severe COVID-19 infection


Plant-based and/or fish (pescatarian) diets may help lower the odds of developing moderate to severe COVID-19 infection, suggest the findings of a six-country study, published in the online journal BMJ Nutrition Prevention & Health.

They were associated with 73% and 59% lower odds, respectively, of severe disease, the findings indicate.

Several studies have suggested that diet might have an important role in symptom severity and illness duration of COVID-19 infection. But, as yet, there’s little evidence to confirm or refute this theory.

To explore this further, the researchers drew on the survey responses of 2884 frontline doctors and nurses with extensive exposure to SARS-CO-v2, the virus responsible for COVID-19 infection, working in France, Germany, Italy, Spain, the UK and the US.

The participants were all part of a global network of healthcare professionals registered with the Survey Healthcare Globus network for healthcare market research. The researchers used this network to identify clinicians at high risk of COVID-19 infection as a result of their jobs.

The online survey, which ran between July and September 2020, was designed to elicit detailed information about respondents’ dietary patterns, based on a 47-item food frequency questionnaire, over the previous year, and the severity of any COVID-19 infections they had had, using objective criteria.

The survey also gathered information on personal background, medical history, medication use, and lifestyle.

The various diets were combined into plant-based (higher in vegetables, legumes, and nuts, and lower in poultry and red and processed meats); pescatarian/plant-based (as above, but with added fish/seafood); and low carb-high protein diets.

Some 568 respondents (cases) said they had had symptoms consistent with COVID-19 infection or no symptoms but a positive swab test for the infection; 2316 said they hadn’t had any symptoms/tested positive (comparison group).

Among the 568 cases, 138 clinicians said they had had moderate to severe COVID-19 infection; 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.

And compared with those who said they ate a plant-based diet, those who said they ate a low carb-high protein diet had nearly 4 times the odds of moderate to severe COVID-19 infection.

These associations held true when weight (BMI) and co-existing medical conditions were also factored in.

But no association was observed between any type of diet and the risk of contracting COVID-19 infection or length of the subsequent illness.

This is an observational study, and so can’t establish cause, only correlation. It also relied on individual recall rather than on objective assessments, and the definition of certain dietary patterns may vary by country, point out the researchers.

Men outnumbered women in the study, so the findings may not be applicable to women, they add.

But plant-based diets are rich in nutrients, especially phytochemicals (polyphenols, carotenoids), vitamins and minerals, all of which are important for a healthy immune system, say the researchers.

And fish is an important source of vitamin D and omega-3 fatty acids, both of which have anti-inflammatory properties, they add.

“Our results suggest that a healthy diet rich in nutrient dense foods may be considered for protection against severe COVID-19,” they conclude.

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

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

He adds:”This study highlights the need for better designed prospective studies on the association between diet, nutritional status and COVID-19 outcomes.”

It is estimated that nearly 75% of the novel human pathogens in the last decades, the majority of which are represented by viruses, have originated in animals [1,2,3]. The pandemic of the coronavirus disease 2019 (COVID-19) has sparked an immediate discussion regarding wildlife trade and evoked various calls to ban the activity or limit it more strictly [4].

This is due to the origin of the causative factor of COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is most likely to be linked primarily with a bat host, with one study demonstrating 96% identity at the whole-genome level to betacoronavirus BatCoV RaTG13 detected in Rhinolophus affinis [5]. However, it is plausible that transmission to humans involved an intermediate host, and some studies have postulated that this strain evolved in pangolins [6].

Nevertheless, wild mammalian and avian species, which are often subject to hunting, can harbor strains belonging to different coronavirus genera and vary in the risk of cross-species transmission [7]. Moreover, a number of other viral pathogens posing a relevant public health threat have emerged in wild animals [4].

For example, the first case of Ebola virus infection in West Africa was likely acquired via exposure to fruit bats [8], the origin of rubella virus is probably also zoonotic (with cyclops leaf-nosed bats indicated as a primary host) [9], whereas human immunodeficiency virus 1 (HIV-1) and HIV-2 are linked to the primary transmission and further mutation of simian immunodeficiency virus from chimpanzee and sooty mangabey monkeys, respectively, during preparation and consumption of their meat [10,11].

It should be emphasized, however, that more strict regulation of hunting and wildlife trade cannot be regarded as the only strategy to prevent future zoonotic spread because the major driver of the emergence of the infectious disease includes the expansion of human settlements in more remote areas, deforestation and expansion of agricultural land, and industrialized livestock production [2,12,13]. The effect of the former substantially increased over the previous decades and will continue to grow due to the forecasted upward trend for meat. Ultimately, increased animal agriculture will contribute to an increased risk of future zoonoses.

The recent report on G4 EA H1N1 in Chinese pigs is highlighting that these animals can serve as intermediate hosts for the generation of influenza viruses with epidemic potential [14]. Furthermore, there are six coronaviruses currently known to be pathogenic to pigs.

These include four members of Alphacoronavirus genus—porcine respiratory coronavirus (PRCoV), porcine epidemic diarrhea virus (PEDV), swine acute diarrhea syndrome-coronavirus (SADS-CoV) and transmissible gastroenteritis virus (TGEV), one member of Betacoronavirus—porcine hemagglutinating encephalomyelitis virus (PHEV), and one member of Deltacoronavirus—porcine deltacoronavirus (PDCoV) [15].

The latter has undergone the recent bird-swine transmission highlighting the potential of some deltacoronaviruses to cross species, also on the avian–mammalian routes. This is due to the fact that within avian deltacoronaviruses the recombination events frequently concern the spike region of the receptor-binding domain [16]. PEDV and SADS-CoV are also emerging swine pathogens [17].

Importantly, the latter, first identified in 2016 [18], has been recently demonstrated to infect and replicate efficiently in several different primary human lung and intestinal cells, and was not neutralized by human sera [19]. All in all, this demonstrates that not only coronaviruses related to wild animals but also to livestock can display the potential risk for future emergence events in the human population. Some mitigation can be offered by continuous surveillance and identification of new viral strains with pandemic potential [4], although this strategy itself does not offer sufficient protection

Other problems with the modern livestock industry, such as outbreaks of African swine fever (ASF) provide an additional impetus for alternative proteins. Given the current lack of vaccines or effective pharmaceuticals (although various efforts are pursued in this regard), ASF is a threat to the swine industry and food security in Europe and Asia [20]. It is also a reminder that unpredicted epidemics in livestock can cause disturbances in global food security.

The other example is avian influenza that causes loss to the international poultry industry and market shares, supply shortages, trade flow disruptions and the loss of consumer confidence [21,22]. Therefore, the search for and implementation of alternative protein sources for food is urgently needed.

It should also be stressed that the range of human infectious agents related to the production of animal products goes beyond viruses and includes bacteria (e.g., mycobacteria and rickettsiae, fecal bacteria), fungi (e.g., microsporidia), parasites (helminths, metazoan, and protozoan), and prions [23]. Moreover, industrial livestock farming is associated with a need to use a variety of veterinary drugs and accounts for more than half of all antibiotic use, discharge of which promotes antibiotic resistance in the environment [24].

Last but not least, the industrial production of animal products can have devastating effects on the environment, encompassing greenhouse emissions, deforestation (including that in the Amazon River Basin, a key component of Earth’s climate system), freshwater withdrawal, eutrophication of aquatic ecosystems, and soil acidification [25].

Given all these threats associated with meat production, as well as the generally insufficient availability of high-quality meat products, especially in developing countries, it is important to consider potential alternatives to animal-derived nutrition. The adoption of plant-based products, insect sources of proteins, as well as ‘cultivated meat’ are important considerations for the future global food supply.

The COVID-19 pandemic is a global public health threat but also a general reminder of severe disturbances related to zoonotic viral epidemics—the risk of which can also be associated with livestock farming. In such a broad context, it should also serve as a call-to-action to mobilize substantial resources and pursue multi-dimensional strategies to prevent future zoonosis, not only when it comes to the control of wildlife trade and consumption (the primary risk factor associated with such diseases), but also the re-evaluation of common food industry practices.

The objective of this paper is to present the potential alternatives to meat production. The paper aims to answer the question of whether plant-based meats, insect-based proteins and cultured meat can provide a solution to the problem and decrease the risk of a future outbreak of zoonoses, but also to discuss the advantages and limitations to their introduction.

Is the Reduction of Meat Consumption a Solution?

Considering that meat consumption of wild or farmed origin is viewed as a potential driver for the emergence of novel zoonoses, one could suggest that its limitation may serve as a solution to minimize the risk of future spill-overs, outbreaks, and pandemics. However, achieving such a goal appears to be unrealistic. The demand for meat is facing a global increase with a worldwide surge over the last six decades [26,27].

The increasing trends are now particularly evident in developing countries. For example, India, often perceived as a household with the largest population of vegetarians [28], is currently experiencing the highest growth rates for meat consumption in the world [29]. According to the recent forecast by the World Economic Forum, global meat consumption will double by 2050. The demand for livestock products will be driven by the growth in population and in incomes, which are accompanied by changing food preferences [30]. The developed countries are still dominated by high levels of food of animal origin, and this is despite the growing appreciation of plant-based diets and the popularity of vegetarianism [31].

One should note that vegetarianism can be manifested by different forms encompassing minimizing (e.g., lacto-ovo-vegetarianism, pescetarianism) or eliminating all animal products completely from the diet (veganism), with the latter being least popular [32]. As recently highlighted, being vegan is often considered odd or deviant in the regions driven by the mainstream norms of carnism [33]. Importantly, however, limiting meat consumption has numerous positive effects beyond the epidemiological realm.

They include personal health benefits, particularly in relation to limiting the consumption of red and processed meat products, which were classified as Group 2A (probably carcinogenic to humans) and Group 1 (carcinogenic to humans) by the International Agency for Research on Cancer, respectively [34]. The well-balanced plant-based diets have shown benefits in terms of prevention and treatment of cardio-metabolic disease, type 2 diabetes and decreasing the total risk of cancer [35,36,37]. On the contrary, the adherence to an unbalanced plant-based diet does come with significant health risks [38,39].

The advantage of such diets is that they are superior ethically, an aspect that plays a significant role in the decision to switch to them for some individuals [40]. Importantly, the plant-based diets are associated with a positive, decreasing effect on the ecological footprint (by lowering the demand on land, water, energy, and reducing greenhouse emissions).

Such advantages cannot be ignored in light of forecasted climate changes [41]. In fact, the report on climate change and land by the Intergovernmental Panel on Climate Change (IPCC) highlights that plant-based diets are a major opportunity for mitigating and adapting to climate change—and includes a policy recommendation to reduce the consumption of meat [42].

Despite it all, plant-based products are likely not able to substitute for those of animal-origin to fulfil the goals (Table 1). This is due to the unwillingness of a relevant percentage of the human population to exclude or limit meat from their diet, challenges to develop the plant-based alternatives that mimic the livestock products in terms of organoleptic parameters and nutritional profile, but also barriers related to cost and safety (e.g., allergenicity in part of population) [43,44,45].

Furthermore, plant-based diets offer a limited alternative for meat-eating pets as they can only be applied in dogs as facultative carnivorous (although it still requires ensuring nutritional adequacy) as opposed to cats which are obligatory carnivores [46,47].

Table 1

Main advantages and disadvantages of approaches discussed in this paper as compared to conventional meat production.

ApproachMain AdvantagesMain Disadvantages
Plant-based dietsLower epidemiological risksIndividual health benefitsLower ecological footprintEthically superiorLow willingness to change the dietAllergenicity in part of the population
Plant-based substitutesDifficulties in mimicking organoleptic properties of meat
Insect-based foodHigh nutritional profileLower ecological footprintEthically more acceptableRisk of pathogen spread in production facilitiesLow consumer acceptance in various parts of the worldChemical hazardsPotential escapes of insects during natural disastersThe risk of viral transmissions yet to be assessed
Cultured meatLower epidemiological risksPredictable productionBetter food securityPotentially lower ecological footprintEthically superiorNumber of technological obstaclesThe economic cost of productionPublic acceptance challenging to predict


More information: Hyunju Kim et al, Plant-based diets, pescatarian diets and COVID-19 severity: a population-based case–control study in six countries, BMJ Nutrition, Prevention & Health (2021). DOI: 10.1136/bmjnph-2021-000272



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