We are now living with Covid 19 and despite most of us having had the vaccine we are picking up the virus frequently. Most of us will throw off symptoms within a few days but some individuals will still have more severe symptoms, may even require hospital admission or develop long covid. Because of this we are understandably still concerned. So why are some people getting more sick and developing long term symptoms?
For the last 3 years I have been researching the gut microbiome and have come across clues as to why this should happen. Studies of patients with severe covid infections and those with long covid have revealed that compositional alterations in the gut microbiome are common to these patients and there were strong associations between gut microbiota composition and the severity of their infection . In particular, a reduction in the relative abundance of certain beneficial bacteria Eg Faecalibacterium prausnitzii , Eubacterium rectale and several Bifidobacterium species has been noted . All of these bacteria are seen in greater abundance in people with healthy and more plant based diets and populations are diminished in those with western diets. These bacteria play important roles in our immune system and in the production of short chain fatty acids – key agents in improving our health .
Non-communicable diseases are those not associated with infections for example Diabetes, obesity, hypertension, chronic lung disease, kidney disease etc. We now know that individuals with non-communicable disease have a greater likelihood of having more severe covid infection and if you have more than one non-communicable disease you are at even greater risk of more severe infection . Again, non-communicable disease is associated with a western diet and lifestyle and to gut microbiota composition.
So gut microbiota composition is strongly associated with the severity of covid and long covid what can we do about it? Well, everyone has a unique gut microbiota which is shaped throughout their life by various things, Eg. mother’s microbiome, birth type, infant feeding choice, exposure to antibiotics, environment that they grew up, exposure to nature, exposure to drugs, too sanitary a lifestyle, exercise, sleep quality, relationships and of course their diet. We risk a disrupting our gut microbiota if we have an unhealthy lifestyle and poor diet and although we cannot change things from our past Eg. our birth, infant feeding choice and previous exposure to antibiotics; we can change what we do now to improve the health of our microbiota.
Our gut microbiome can change fairly dramatically in response to diet change as shown in a study by O’Keefe et al 2015  where he demonstrated that he could completely change the microbiota of rural African’s and African American’s within 2 weeks of diet change. Other studies have also demonstrated similar findings for example a change from western diet to a Mediterranean diet in obese individuals helped to improve diversity of species and restore many keystone species that were lacking prior to the intervention .
What can we eat to improve the health of our gut microbiota? We now understand the huge role that fibre plays by stimulating the growth of beneficial strains of bacteria which ferment fibre to produce short chain fatty acids . These essential metabolic by products which help us improve fat and sugar metabolism, aid our immune function, produce important vitamins and hormones among other important roles. Fibre is derived from plants and it turns out that each different plant will attract a different species of bacteria so the wider variety of plants we eat the more diverse and rich our gut microbiota will become . Polyphenols are organic compounds found in plants which are metabolised by our gut microbiota. They are antibacterial towards harmful bacteria and encourage the growth of beneficial bacteria. We find polyphenols in foods such as olives, berries, pomegranate, cocoa, herbs, spices, tea and coffee . In contrast the fatty and sugary processed foods in our western diet are associated with dysbiosis of the gut . We use many chemicals in processed foods and its no great surprise that many of these are harmful to our gut microbiota Eg. emulsifiers and sweeteners [10,11]. Even simple processing of foods can alter the effect of food on the gut microbiota as found by Holcher et al 2018  where consuming whole nuts resulted in enhancement of the gut microbiota whilst the same quantity of nut butter had no beneficial impact on the gut microbiota as the nut butter was all absorbed in the small bowel and did not reach the large bowel to impact the colonic organisms. Fermented foods can add beneficial bacteria as well as their metabolic by products into our gut and different fermented foods will contain varying quantities of these organisms. Essentially a daily ingestion of probiotic containing foods can keep your good bacteria topped up but they won’t remain in your gut when you stop eating them .
Covid-19 has been devastating to so many people and with the rise in obesity and non-communicable diseases in the western world its not surprising we have not fared well with it. There is a strong correlation between our lifestyle and especially diet and the health of our gut microbiota. Unsurprisingly the relationship between our diet quality and severity of covid has been confirmed in a recent study by by Merino et al 2021 . A diet with a wide variety of whole foods mainly plants whilst avoiding processed foods may help improve gut microbiota composition and function, improve our immune function and reduce the severity of the Covid-19.
** Please consult your healthcare professional before implementing specific diet plans.
- Yuen Kit Yeoh et al. Gut Microbiota composition reflects disease severity and dysfunctional immune responses in patients with covid-19. Gut. 2021;70;698-706. https://doi.org/10.1136/gutjnl-2020-323020
- Chong Pei et al; The Microbiome and Irritable Bowel Syndrome -A Review on the Pathophysiology, Current Research and Future Therapy. Frontiers in Microbiology. 2019;10 https://doi.org/10.3389/fmicb.2019.01870
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- Merino J. Et al. Diet quality and risk and severity of Covid-19: a prospective cohort study. Gut. 2021;70; 2096-2104. https://doi.org/10.1136/gutjnl-2021-325353