RAC member, Dr Shireen Kassam, considers how more plant-based ways of eating will improve health outcomes during and beyond the current pandemic.
Healthcare professionals in the front line of the pandemic response quickly observed that people with underlying chronic health conditions had a greater risk of developing severe COVID-19, requiring hospitalisation, intensive care treatment and ultimately dying. These underlying health conditions were noted to be associated with a number of modifiable risk factors and included overweight and obesity, cardiovascular disease, cancer and type 2 diabetes. In the UK, more than 90%[1] of those who died in the first wave of the pandemic had at least one underlying chronic condition. In the US, 64% of the risk[2] of hospitalisation from COVID-19 was attributable to 4 underlying health conditions: hypertension, heart failure, type 2 diabetes and obesity. These conditions are intimately related to four modifiable lifestyle factors: tobacco smoking, excessive alcohol consumption, lack of physical activity and unhealthy diets.
Back in 2019, a large analysis from the Global Burden of Disease study group reported that unhealthy diets[3] were responsible for 20% of deaths globally every year, mainly from cardiovascular disease, cancer and type 2 diabetes, and thus unhealthy diets were now responsible for more deaths than any other risk factor in the world. These unhealthy diets were typically too high in processed and animal-derived foods and too low in healthy plant foods.
Whilst at the start of the pandemic we were all told to stay at home, physically distance and pray that we were not exposed to the pandemic virus, many clinicians and researchers began to write about the benefits of a healthy diet[4] for supporting the immune system and improving our defences against the pandemic virus. Most of this advice was empirical and based on evidence from other respiratory infections in which bioactive compounds found in fruits, vegetables, herbs and spices, such as vitamin C, flavonoids, caratonoids and curcumin, were associated with reduced severity and better outcomes. In addition, it was hypothesised that a healthier gut microbiome[5] may be important given our knowledge of the gut-lung axis and its involvement in mounting a robust immune response. Many organisations, including my own, Plant-Based Health Professionals UK[6], have been advocating for the widespread adoption of a healthy whole food plant-based diet in line with recommendations from the American College of Lifestyle Medicine[7]. Such a diet is based around equal proportions of fruits, vegetables, whole grains, beans and a small portion of nuts and seeds on most days. This could otherwise be called a healthy or whole food vegan diet. Not only is a whole food plant-based diet beneficial for the prevention and treatment of chronic conditions, but it can also support a healthy immune system, gut microbiome and is environmentally sustainable. The good news is that is possible to see results in a matter of weeks when transitioning to a whole food plant-based diet, with measurable changes in the gut microbiome, reductions in blood pressure and body weight and improvements in insulin resistance and normalisation of blood glucose levels.
A year and a half into the pandemic we now have a scientific basis from which to make these recommendations. It was initially observed that the composition of the gut microbiome[8] in people with COVID-19 was significantly altered compared to people without the infection. This included lower quantities of bacteria associated with the regulation of the immune system. In addition, these alterations were more pronounced in patients with a severe disease course and were associated with higher levels of inflammatory markers in the blood. It’s worth remembering that the American Gut Project[9], one of the largest studies to evaluate the human gut microbiome, has observed that people consuming more than 30 different types of plant foods a week have a healthier and more diverse gut microbiome than people consuming less than 10 different plant types.
The first publication[10] to highlight the importance of a healthy plant-based diet pattern reported the results of a case-control study of healthcare workers, mostly physicians, with significant exposure to COVID-19 patients from six countries. Participants completed a web-based survey from 17 July to 25 September 2020. Information was collected on basic demographic characteristics, past medical history, medications, lifestyle, and COVID-19 symptoms, and a 47-item food frequency questionnaire. The questions captured the dietary patterns of participants over the prior 1 year and included 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. For the analysis, ‘whole foods, plant-based’ diets and ‘vegetarian’ diets were placed into one category called ‘plant-based diets’ (n=254). For the pescatarian diet, data were combined from those following a whole foods plant-based, vegetarian and pescatarian diets, the latter only being 40 participants (n=294). The study included 568 COVID-19 cases and 2316 controls. Those participants who had had COVID-19 were asked to rate the severity based on 5 options from very mild to critical, requiring intensive care.
The results showed that those following a plant-based diet pattern had a 73% reduction in the risk of moderate or severe COVID-19 and those following a pescatarian diet had a 59% reduction in risk. This was independent of body mass index and underlying chronic health conditions. In contrast, participants following a high protein, low carbohydrate diet had 3-fold higher odds of moderate or severe COVID-19 when compared to the plant-based group.
We do have to accept the major limitations of this study when extrapolating these results to a healthy plant-based or vegan diet. This was not a study of people following a vegan or 100% plant-based diet, despite the media headlines suggesting the contrary. In fact, those classified as plant-based were not that healthy, consuming a median of 3.7 portions of legumes and 9.8 portions of fruits per week and still consuming some animal foods, including similar amounts of dairy and eggs to the non-plant-based group, and similar amounts of refined grains. However, their consumption of legumes, nuts and vegetables was significantly higher and consumption of red/processed meat, sugar-sweetened beverages and alcohol significantly lower than those participants who did not follow a plant-based diet. Furthermore, this is not a robust study design being a case-control study, with self-reported dietary data and no set definition of low-carb or plant-based. The impact of residual confounding cannot be excluded and people with more severe COVID-19 may not have been able to participate. In addition, the participants were mainly male, Caucasian physicians.
The second paper[11] published as a pre-print in July 2021 reports data from the now well publicised Zoe COVID symptom study[12]. The paper analysed diet quality in more than half a million participants from the US and UK. During the follow-up period, 31,815 COVID-19 cases were documented. Adherence to a healthy plant-based diet was calculated using the healthy plant-based diet index[13] which gives positive marks to healthy plant foods and negative marks to unhealthy plant foods and all animal foods. Those eating a healthy plant-based diet as defined by the healthy plant-based diet index had a 10% reduction in risk of getting COVID-19 and a 40% reduction in getting severe disease. The impact of a healthy diet was greatest in those from lower socioeconomic groups and independent of underlying chronic health conditions, body mass index, smoking and physical activity. Based on these results, it was calculated that nearly a quarter of COVID-19 cases could have been prevented if these differences in diet quality and wealth had not existed. Of course, this is also not a perfect study. It is observational with self-selected participants, self-reported dietary information and for the primary outcome of COVID-19 infection, a validated symptom-based algorithm was used rather than PCR test results. However, this is likely to be the best evidence we can expect to have outside of a randomised study. The authors conclude
‘Our data provide evidence that a healthy diet was associated with lower risk of COVID-19 and severe COVID-19 even after accounting for other healthy behaviors, social determinants of health, and virus transmission measures’.
Based on the available evidence, we can safely say that any shift to a more plant-based way of eating will improve health outcomes during and beyond the current pandemic. This has been further highlighted, to some degree at least, in the second part of the UK National Food Strategy[14] which recommends that UK citizens should significantly decrease meat consumption whilst significantly increasing the consumption of fruits, vegetables and fibre. A shift to a plant-based diet is also essential to deal with the global climate and ecological crises we are facing. Health professionals[15] have been ‘called to action’; ‘Without decisive and urgent action, the climate crisis will increasingly undermine human health and disrupt healthcare delivery. There are both moral and practical reasons for health professionals to be at the forefront of climate action.’ Part of this action[16] is to support citizens to adopt a healthy and sustainable diet, starting with elimination of foods that cause the greatest harm to human and planetary health, processed and unprocessed red meat[17]. With the growing body of evidence, I hope we are nearing a time when the default diet[18] recommended by all healthcare professionals is a plant-based one.
Written by Dr Shireen Kassam
References
1. Williamson, E.J. et al. Factors associated with COVID-19 related death using OpenSAFELY. Nature 2020; 584: 430 – 436.
2. O’Hearn, M et al. Coronavirus Disease 2019 Hospitalizations Attributable to Cardiometabolic Conditions in the United States: A Comparative Risk Assessment Analysis. Journal of the American Heart Association 2021; 10 (5).
3. Afshin, A. et al. Health effects of dietary risks in 195 countries, 1990 – 2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet 2019; 393 (10184): 1958 -1972.
4. Calder, P.C. Nutrition, immunity and COVID-19. BMJ Nutrition, Prevention & Health 2020; 3 (1).
5. Zheng, D., Liwinski, T. & Elinav, E. Interaction between microbiota and immunity in health and disease. Cell Research 2020; 30, 492 - 506.
6. Plant Based Health Professionals. (accessed 12th August 2021)
7. Tips, J. American College of Lifestyle Medicine Announces Dietary Lifestyle Position Statement for Treatment and Potential Reversal of Disease. (accessed 12th August 2021).
8. Yeoh, Y.K et al. Gut Microbiota composition reflects disease severity and dysfunctional immune responses in patients with COVID-19. Gut 2021; 70: 698–706 (accessed 12th August 2021)
9. McDonald, D et al. American Gut: an Open Platform for Citizen Science Microbiome Research. mSystems 2018; 3 (3) American Gut: an Open Platform for Citizen Science Microbiome Research (asm.org) (accessed 12th August 2021)
10. Kim, H et al. Plant-based diets, pescatarian diets and COVID-19 severity: a population-based case-control study in six countries. BJM Nutrition, Prevention & Health 2021 (accessed 12th August 2021)
11. Merino, J. et al. Diet quality and risk and severity of COVID-19: a prospective cohort study. (accessed 12th August 2021)
12. ZOE Covid Study. (accessed 12th August 2021)
13. Satija, A. et al. Healthful and Unhealthful Plant-Based Diets and the Risk of Coronary Heart Disease in U.S. Adults. Journal of the American College of Cardiology. 70 (4) 411-422. (accessed 12th August 2021)
14. National Food Strategy. (accessed 12th August 2021)
15. Salas, R.N et al. A pathway to net zero emissions for healthcare. BMJ 2020; 371 (accessed 12th August 2021)
16. Declaration Calling for Family Doctors of the World To Act on Planetary Health. (accessed 12th August 2021)
17. Freeman, L. & Kassam, S. Why Family Doctors Should Support Patients to Remove Red Meat From the Diet. (accessed 12th August 2021)
18. Storz, M. Will the plant-based movement redefine physicians’ understanding of chronic disease? The New Bioethics 2020; 26: 141 – 157.
The views expressed by our Research News contributors are not necessarily the views of The Vegan Society.
