Covid-19 and Diet – Are we Eating Ourselves Sick?

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We are 2 years into a pandemic that has forever altered our lives. At the time of writing this article, over 5.5 million lives have been lost globally to covid-19,(1) with many others left permanently affected with chronic fatigue, dyspnoea, sleep disturbances, anxiety and/or depression, and permanent loss of taste/smell,(2) to name a few. We have been scrambling for vaccinations, covertly acquiring ivermectin in case of personal infection, and have been controlled by public health measures and lockdowns aimed at reducing the spread of Covid-19.

However, one message that has failed to be conveyed to the public, is the importance of diet and lifestyle in the co-management and prevention of diseases such as Covid-19. In the early phases of a pandemic, it is understandable and justifiable to focus on immediate methods of minimising the spread of the infection, and on treatment options to minimize the morbidity and mortality of the infection. Nonetheless, we are two years in, and we are still not having enough conversations about the role that our individual health plays in fighting off diseases such as Covid-19.

It has been demonstrated that aside from non-modifiable risk factors such as sex and age, modifiable risk factors including hypertension, diabetes mellitus, chronic kidney disease (CKD), and cardiovascular disease (CVD) are significant risk factors for severe Covid-19 disease and death.(3) All of which, barring CKD, constitute the top 10 killers in South Africa.(4)

One risk factor that is infrequently mentioned or discussed, likely because it remains frustratingly controversial, is obesity. As we’ve seen in prior respiratory virus pandemics, as well as during the Covid-19 pandemic, obesity not only presents itself as an independent risk factor for severe infection, but also poses a challenge for mechanical ventilation due to reduced lung volumes resulting from increased intra-abdominal pressure from excess adipose tissue.(5) People that classify as obese, also have more of a restricted pattern of breathing, due to the excess adipose tissue accumulation in the chest and abdominal cavities, preventing the lungs from expanding normally.(6)

So why are we not more aggressively targeting the prevention and optimization of management of these diseases, as that would surely translate into improved health outcomes during a pandemic? There have been several influenza pandemics over the past century, and there will be more to come. The time to concentrate more focus on diseases of lifestyle, was yesterday.

Is there a connection between plant-based diets and Covid-19?

Shortly after the pandemic started to spread from Wuhan, China, into other countries in Europe, researchers studied almost 3000 health care workers in high-risk environments, to determine if their diet had an impact on their rate of infection or disease severity. Over 2 months, over 500 Covid-19 cases were reported, and a plant-based diet (PBD) was associated with a 73% lower risk of moderate-severe Covid-19, while a spectrum of plant-based diets (including vegetarian and pescatarian diets), was associated with a 53% lower risk. Conversely, low-carbohydrate, high-protein diets were associated with a 48% greater chance of moderate-severe Covid-19 disease. Interestingly, when they looked at only the cases that were confirmed by means of a PCR or antibody test, those following plant-based diets also had a lower chance of becoming infected at all.(7)

Many of you may have heard of the “blue zones” which are areas with the longest living people in the world, all of which eat plant-predominant diets, high in carbohydrates from whole foods and low in animal products and processed foods. Okinawa in Japan is one of these blue zones, and their Covid-19 death rate was 1/16th that of Tokyo, Japan (0.08% vs 1.3% respectively).(8)

What is the role of plant-based diets in the prevention and management of diseases of lifestyle?

Hypertension. There are several studies linking PBD with improved blood pressure (BP) control. The EPIC-Oxford study, that looked at over 57000 men and women in the UK, found that as people removed meat and other animal products from their diets, their rates of hypertension decreased, with omnivores having the highest prevalence of hypertension, and vegans having the lowest prevalence, with pescatarians and lacto-ovo-vegetarians in between.(9) The Coronary Artery Risk Development in Young Adults (CARDIA) study was a prospective study that followed over 5000 men and women aged 18-30 years for 15 years. A CARDIA sub study compared dietary factors and the incidence of elevated blood pressures. They found that the consumption of plant foods, particularly whole grains, fruits and nuts, had an inverse association with the development of elevated BPs, while red and processed meat were directly associated with elevated BPs.(10) Another study combined the data from 3 large prospective cohorts, the Nurses Health Study I, the Nurses Health Study II, and the Health Professions Follow Up Study, amounting to over a million person-years of follow up. Pooled data from these 3 studies showed that eating meat once a day or more increased the risk of hypertension by 30% compared to eating meat less than once per month, and this was independent of whole grain, fruit or vegetable intake, meaning that eating meat with these foods did not mitigate that risk.(11) And finally, a meta-analysis of 7 controlled trials and 32 observational studies also showed that vegetarian diets were associated with lower blood pressures.(12)

Chronic Kidney Disease. Your kidneys are responsible for filtering many waste products and excess fluid from the body. Chronic kidney disease describes has a gradual, progressive loss of kidney function, which eventually becomes life threatening. As the kidneys become damaged, from hypertension or diabetes for example, they start to leak protein into the urine, known as proteinuria, which is a strong indicator for the progression of CKD.(13) Whole food plant-based diets (WFPBD) exclude animal products, as well as highly processed foods such as oils, sugars and refined carbohydrates, and are rich in fruits, vegetables, whole grains, nuts, seeds and legumes. By nature, this diet is high in fiber, and a 2015 review of 14 controlled feeding trials showed that dietary fiber was associated with lower levels of urea and creatinine (elevated levels of these two blood tests are markers of kidney dysfunction), with a dose-dependent response for creatinine (meaning the more fiber they ate, the lower their creatinine was).(14) Diets based on animal products have been shown to induce hyperfiltration (which overworks the kidneys) and is associated with progression of CKD.(15) While WFPBD are generally lower in protein, which is recommended for individuals with CKD,(13). Clinical trials have also demonstrated that vegetarian diets reduce proteinuria when compared to animal-based diets.(16)

Type 2 diabetes mellitus. Plant-based foods such vegetables, whole grains and fruit (yes fruit!) have a protective effect against the development of type 2 diabetes mellitus (DMII), while animal products, such as red meat, processed meat and eggs have been shown to increase the risk of DMII.(17) The Rotterdam study from the Netherlands showed that plant-based diets were protective against the development of DMII, as well as pre-diabetes, and that this effect was enhanced the more individuals ate plant-based whole foods rather than processed vegan foods.(17) A pooled analysis of the Nurses Health studies 1 and 2 and the Health Professionals Follow-up Study looked at over 16000 incident cases of DMII, and also found that a plant-based diet was protective against the development of DMII when compared to vegetarian and omnivorous diets. And again, the more healthful the plant-based diet, the greater the protective effect.(18) Not only do plant based diets lower the risk of developing DMII, but they also improve glycaemic (blood sugar) control, help to mitigate the risk of ischaemic heart disease in diabetic patients, improve kidney function in CKD patient, and can even reduce the pain associated with diabetic neuropathy (damage to the nerves caused by diabetes that results in painful burning or pins and needles in the feet and hands).(16)

Cardiovascular disease. It has long been known that vegans and vegetarians have a lower risk of heart disease. The EPIC-Oxford study showed that vegetarians had a 32% lower risk of ischaemic heart disease (IHD) than non-vegetarians after adjusting for other risk factors such as smoking and alcohol.(19) Another large review of 5 pooled prospective cohorts found that vegetarians had a 24% lower mortality than non-vegetarians from ischaemic heart disease.(20) In terms of interventions, the Lifestyle Heart Trial was a randomized controlled trial that implemented lifestyle changes including a 10% low-fat vegetarian diet, and compared it with controls. After 1 year, the experimental (vegetarian) group had a 91% reduction in anginal (chest pain) episodes, compared to an increase in the control group. And repeat coronary angiograms showed a reduction in the degree of coronary artery stenosis (narrowing of the arteries supplying the heart). There were also fewer heart attacks and interventions needed in the experimental group.(21) Similarly, Lyon Diet Heart Study used a Mediterranean diet as an intervention in a randomized control trial, and found that after 46 months of follow up, the Mediterranean diet group had a substantially lower rate of heart attacks and death compared to the control group.(22)

Obesity. The Adventist Health Study-2 reported an average BMI difference of 5 units between vegans and omnivores,(23) while several studies have shown vegan diets to be more effective for weight loss than lacto-ovo-vegetarian diets and omnivorous diets.(24,25)

In conclusion, we have evidence that plant-based diets may be protective against becoming infected with the Covid-19 virus, as well as against moderate-severe Covid-19 disease once infected, and we also have substantial evidence that plant-based diets reduce the risk of developing and are effective in managing the risk factors for severe Covid-19 disease. These findings should hopefully serve as a conversation starter regarding both the usefulness of PBD in the prevention and management of both diseases of lifestyle and infectious diseases, as well as our individual responsibility to influence our health outcomes during pandemics such as Covid-19.

References

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