Diet and COVID-19; is there a link?

Healthcare professionals have been promoting the role of healthy diets from the very start of the COVID-19 pandemic. This was on the basis of prior evidence that a nutrient-dense diets, full of vitamins, antioxidants, anti-inflammatory and other bioactive compounds not only reduce the risk of developing chronic health conditions but has been shown to reduce the severity of acute infections too. At the time there wasn’t any specific evidence that diet would help in the fight against COVID-19, but clearly there was no downside. It is well known that a healthy diet can at the very least help support the functioning of the immune system. Some of the important nutrients for the immune system are listed in the table below.

Chronic health conditions increase the risk of severe COVID-19

What became apparent early on in the pandemic was 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% 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 of hospitalisation from COVID-19 was attributable to 4 underlying health conditions: hypertension, heart failure, type 2 diabetes and obesity. We know that dietary factors play a large role in the development of these underlying conditions, with diets high in meat and processed foods whilst being low in healthy plant foods being the main culprit.

High blood cholesterol and glucose increases the severity of COVID-19

Scientists have further shown that high cholesterol and high blood glucose, conditions that are more likely with a meat-based Western-style diet pattern drive every stage of the pandemic virus making it more likely to infect cells and progress to a more severe illness. A healthy plant-based diet is of course the easiest way to keep cholesterol and glucose at normal levels.

A healthy gut microbiome is essential for a healthy immune system

A healthy immune system requires a healthy gut and specifically a healthy gut microbiome. The trillions of micro-organisms in our gut are crucial for fighting infection, affecting the immune system of every organ, and rely on a healthy fibre-rich, plant-based diet. There is even communication between the gut microbes and the lung, known as the gut-lung axis.

A year and a half into the pandemic researcher’s observed that the composition of the gut microbiome 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, 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.

Plant-based diets reduce COVID-19 severity in healthcare workers

The first publication to highlight the importance of a healthy plant-based diet for reducing the severity of COVID-19 was a study of healthcare workers from six countries, mostly physicians, with significant exposure to patients with COVID-19. Researchers collected information on basic demographic characteristics, past medical history, medications, lifestyle, and a history of COVID-19 infection and its severity. All participants completed a dietary questionnaire from which they were classified into different diet groups including, whole foods, plant-based diet; keto diet; vegetarian diet; Mediterranean diet; pescatarian diet; Palaeolithic diet; low fat diet; low carbohydrate diet; high protein diet. 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 a 3-fold higher risk of moderate or severe COVID-19 when compared to the plant-based group.

It should be noted though that this was not a study of vegans or those following a 100% plant-based diet. In fact, those classified as plant-based were not that healthy, consuming only 3.7 portions of legumes and 9.8 portions of fruits per week and still consuming some animal foods. 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. Nonetheless, this study has provided the first evidence to suggest that a healthy diet higher in plant foods may be a useful tool to reduce the impact of COVID-19.

A healthy plant-based diet reduces the risk and severity of COVID-19

The second paper reports data from the now well publicised Zoe COVID symptom study. The paper analysed diet quality in more than half a million participants from the US and UK, 31,815 of whom had COVID-19. Adherence to a healthy plant-based diet was calculated using the healthy plant-based diet index which gives positive marks to healthy plant foods and negative marks to unhealthy plant foods and all animal foods. Participants eating a healthy plant-based diet were shown to have 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. Once again, this is not a perfect study as it is only observational and cannot prove cause and effect. Nonetheless, 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 behaviours, social determinants of health, and virus transmission measures’.

Conclusions

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 will  also help prevent the next potential pandemic, given that most new and emerging infectious threats are a consequence of our treatment of non-human animals, be it the wildlife trade, destruction of wildlife habitats or intensive ‘factory’ farming.

For those who are still sceptical about the need to move to a plant-based food system, I urge you to watch the latest documentary, Eating Our Way to Extinction, demonstrating the destruction caused by our current diet habits. I was honoured to have played a small part in this documentary. 

With the growing body of evidence, I hope we are nearing a time when the default diet recommended by all healthcare professionals and civil society is a plant-based one. At plant-based health online we help our patients and clients adopt a healthy and sustainable diet and lifestyle so they can achieve their best health.

by Dr Shireen Kassam, Co-founder Plant-Based Health Online