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Nutrition in the time of COVID-19

As the world grapples with the novel coronavirus pandemic, Doctors For Nutrition’s Western Australia Lead Nutritionist, Dr Angela Genoni PhD, unpacks the role of nutrition in supporting our immune system.

Fruit image

The novel coronavirus SARS-CoV-2 and its resulting disease, COVID-19, have already touched almost every country on the globe. Many of us have lost jobs, had hours reduced and are being urged or required to stay home in lockdown, unless we work in healthcare or other essential industries.

Things that seemed secure a few short weeks ago are no longer quite so safe; many of us have necessarily been brought back to living simple lives. When we stop to reconsider the basics, it is important to consider the role that good nutrition plays in supporting our immune system.

So, what do we really need to support our immune system? What evidence is there surrounding what we eat and the ability of our immune system to cope with viral or bacterial infections (the latter of which often occur when a person is already fighting a viral disease such as COVID-19)?

Western diets and susceptibility to infection

As stated in the latest United Nations System Standing Committee on Nutrition newsletter, “Unhealthy diets are the leading cause of ill-health. Without dedicated action on nutrition, all forms of malnutrition are likely to increase as a result of the pandemic’s impact on food environments. Financial hardships, reduced physical activity, and altered purchasing patterns favouring products with longer shelf life and often poorer nutrition profiles can lead to higher levels of food insecurity, undernutrition, and overweight/ obesity.”[1]

Here in Australasia, we live in a society where we can purchase whatever food we like at almost any time we wish. Unfortunately, much of this is of animal origin and/or highly processed, making it highly palatable and yet lacking in vital micro and macronutrients. The result is a perverse form of malnutrition where, despite the overabundance of food, people are chronically under-nourished.

The over-abundance of nutritionally-poor food in our Western society is a proven trigger for inflammation that contributes to immune dysfunction and reduced control of infection.[2] This over-abundance also contributes to a prolonged positive energy balance which is one of the primary drivers of obesity.[3,4] Fat cells (adipocytes) release inflammatory substances such as tumour necrosis factor (TNF) and the Interleukins (IL), particularly IL-1 and IL-6, and these inflammatory markers combined with obesity, greatly increases susceptibility to infection.[4]

Angela Genoni, PHD
Dr Angela Genoni PhD

Western style diets, characterised by a high-fat content, are well reported in the scientific literature to alter the colonic microbiome in favour of an undesirable shift to a higher ratio of Firmicutes:Bacteriodetes.[5-7] This is associated with increased gut permeability, an increase in serum lipopolysaccharide (LPS) concentrations, and reductions in bacterial by-products (including short chain fatty acid production), all of which can result in chronic inflammation and decrease the ability to fight infection. This is supported by literature showing obesity to be an independent risk factor for morbidity and mortality following infection with the 2009 H1N1 influenza A virus.[4] Early data from the COVID-19 pandemic indicates the risk of complications from COVID-19 are also increased in patients with a BMI over 25.[8]

Similarly, a modern Western-style diet has been shown to induce significant shifts in our gut microbiome and is strongly associated with weight gain and associated metabolic disorders.[9] Evidence now also shows the gut microbiome exhibits an ability to talk with the lung microbiome, termed the gut-lung axis, which may also influence our ability to

respond to triggers such as viral infections.[10] Diets high in plant-based foods with varieties of dietary fibre types are considered beneficial for host health due to their ability to increase microbial diversity.[11, 12] In addition to the microbial populations, the metabolites produced, such as short chain fatty acids, may provide some protection against inflammatory responses.[13]

We also know that a single meal containing high amounts of salt and saturated fat increase the inflammatory response in those with asthma, irrespective of BMI.[14]

Nutrition Label

The protective properties of whole food plant-based diets

The ‘why’

The risk factors outlined above make it very prudent to consider what sort of diet we can follow to reduce our risk of inflammation, both after single meals and over the long term. Diets high in dietary fibre (obtained exclusively from plants), are well reported to reduce inflammation.[17, 18] A particular type of dietary fibre, resistant starch, is showing particular promise for reducing gut and systemic inflammatory markers.[19, 20] Resistant starch is found abundantly in foods such as whole grains, legumes and root vegetables. [6] Plant-based diets have also been shown to consistently improve obesity-related inflammatory profiles.[15, 16]

Plant foods also contain many other bioactive substances, such as flavonoids, whose significance we are only beginning to understand, both individually and synergistically, in regulating many biochemical pathways – including inflammation – in the body.[16, 21]

The ‘how’

In these uncertain times, it is relatively easy and cost effective to base your diet around plant foods and gain the health benefits of dietary fibre and bioactive substances. Dried whole grains and legumes are perfect sources of complex carbohydrates, dietary fibre and resistant starch. Generally, these foods are readily available and cost effective, even in our current state of lockdown. Basing your diet on this food group and adding in fruits and vegetables will provide all of your nutritional needs, including protein.*

A simple diet, based on simple foods can also result in significant cost savings in these stressful times.[22] Contrary to popular belief, frozen vegetables are not nutritionally inferior. Often snap-frozen at the point of harvest, in some cases they can contain more nutritional benefit than their fresh counterparts due to being frozen so quickly.[23]

Rainbow Vegetables

Other protective lifestyle factors

Finally, our immune system is not solely influenced by what we eat. Long-term stress is also well reported to detrimentally impact our immune system.[24] We are all under varying degrees of stress during this crisis and it is vitally important we stop momentarily to put ourselves first and try to relax. We know many people in healthcare and other essential services are working extra hours under high stress, while many others are facing the stress of financial uncertainty. Hard as it may feel, this makes it even more important than ever to find ways to unwind. Now is the ideal time to start a small but sustainable practice of meditation, or just put some music on to relax. We all need the support of friends, loved ones and strangers now more than ever, so again, now is a crucial time to practise kindness and find ways to look after each other, even if those are limited to ‘virtual’ methods.[25]

Similarly, lack of sleep is also undesirable for optimal immune function,[26] so do try to make this a priority. For those who are, of necessity, spending more time at home, the current situation is an opportunity to be kind to your body and catch a bit of extra time in bed.

It may be a little more difficult for many of us to follow our regular exercise routines whilst COVID-19 still dominates our society, with gyms, swimming pools and beaches closed. However, exercise has many benefits for our physical and mental wellbeing, and may also further support our dietary pattern in terms of a healthy gut microbiome.[27] There are many forms of exercise attainable at home at little to no cost and again, it is about finding something small which fits with your lifestyle to start with.

As I like to tell my children, “we get one body and one chance at a long-healthy life. Look after it.”

*Long-term plant-based diets require supplementation with vitamin B-12

  1. United Nations System Standing Committee on Nutrition. Email, 28 March 2020. Food Environments in the COVID-19 Pandemic: Impacts and positive policy actions to deliver sustainable healthy diets for all
  2. Myles IA. Fast food fever: reviewing the impacts of the Western diet on immunity. Nutrition Journal. 2014;13(1):61.
  3. Apovian CM. Obesity: definition, comorbidities, causes, and burden. Am J Manag Care. 2016;22(7 Suppl):s176-85.
  4. Milner JJ, Beck MA. The impact of obesity on the immune response to infection. Proc Nutr Soc. 2012;71(2):298-306.
  5. Clemente JC, Ursell LK, Parfrey LW, Knight R. The impact of the gut microbiota on human health: an integrative view<. Cell. 2012;148(6):1258-70.
  6. Genoni A, Christophersen CT, Lo J, Coghlan M, Boyce MC, Bird AR, et al. Long-term Paleolithic diet is associated with lower resistant starch intake, different gut microbiota composition and increased serum TMAO concentrations. European journal of nutrition. 2019:1-14.
  7. Turnbaugh PJ, Bäckhed F, Fulton L, Gordon JI. Diet-induced obesity is linked to marked but reversible alterations in the mouse distal gut microbiome. Cell host & microbe. 2008;3(4):213-23.
  8. World Obesity Federation. Coronavirus (COVID-19) & Obesity. World Obesity Federation; 2020.
  9. Zinöcker MK, Lindseth IA. The Western diet–microbiome-host interaction and its role in metabolic disease. Nutrients. 2018;10(3):365.
  10. Anand S, Mande SS. Diet, Microbiota and Gut-Lung ConnectionFront Microbiol. 2018;9:2147.
  11. Simpson HL, Campbell BJ. Review Article: Dietary fibre–microbiota interactions. Alimentary pharmacology & therapeutics. 2015;42(2):158-79.
  12. Xu D, He G, Mai K, Zhou H, Xu W, Song F. Postprandial nutrient-sensing and metabolic responses after partial dietary fishmeal replacement by soyabean meal in turbot (Scophthalmus maximus L.). British Journal of Nutrition. 2016;115(3):379-88.
  13. Vinolo MA, Rodrigues HG, Nachbar RT, Curi R. Regulation of inflammation by short chain fatty acids. Nutrients. 2011;3(10):858-76.
  14. Wood LG, Garg ML, Gibson PG. A high-fat challenge increases airway inflammation and impairs bronchodilator recovery in asthma. J Allergy Clin Immunol. 2011;127(5):1133-40.
  15. Eichelmann F, Schwingshackl L, Fedirko V, Aleksandrova K. Effect of plant‐based diets on obesity‐related inflammatory profiles: a systematic review and meta‐analysis of intervention trials. Obesity Reviews. 2016;17(11):1067-79.
  16. Liu RH. Health benefits of fruit and vegetables are from additive and synergistic combinations of phytochemicals. The American Journal of Clinical Nutrition. 2003;78(3):517S-20S.
  17. Kim MS, Hwang SS, Park EJ, Bae JW. Strict vegetarian diet improves the risk factors associated with metabolic diseases by modulating gut microbiota and reducing intestinal inflammation. Environmental Microbiology Reports. 2013;5(5):765-75.
  18. Roager HM, Vogt JK, Kristensen M, Hansen LBS, Ibrügger S, Mærkedahl RB, et al. Whole grain-rich diet reduces body weight and systemic low-grade inflammation without inducing major changes of the gut microbiome: a randomised cross-over trial. Gut. 2019;68(1):83-93.
  19. Brouns F, Kettlitz B, Arrigoni E. Resistant starch and “the butyrate revolution”. Trends in Food Science & Technology. 2002;13(8):251-61.
  20. Jacobasch G, Schmiedl D, Kruschewski M, Schmehl K. Dietary resistant starch and chronic inflammatory bowel diseases. International journal of colorectal disease. 1999;14(4-5):201-11.
  21. Bellik Y, Boukraâ L, Alzahrani HA, Bakhotmah BA, Abdellah F, Hammoudi SM, et al. Molecular mechanism underlying anti-inflammatory and anti-allergic activities of phytochemicals: an update. Molecules. 2013;18(1):322-53.
  22. Schuster, R. How to Get People to Stop Eating Meat? Better Alternatives. Haaretz. May 18, 2017
  23. Favell D. A comparison of the vitamin C content of fresh and frozen vegetables. Food chemistry. 1998;62(1):59-64.
  24. Dhabhar FS. Effects of stress on immune function: the good, the bad, and the beautiful. Immunologic research. 2014;58(2-3):193-210.
  25. World Health Organization. Mental health and psychosocial considerations during the COVID-19 outbreak. 18 March 2020
  26. Tobaldini E, Costantino G, Solbiati M, Cogliati C, Kara T, Nobili L, et al. Sleep, sleep deprivation, autonomic nervous system and cardiovascular diseases. Neuroscience & Biobehavioral Reviews. 2017;74:321-9.
  27. Ticinesi A, Lauretani F, Tana C, Nouvenne A, Ridolo E, Meschi T. Exercise and immune system as modulators of intestinal microbiome: implications for the gut-muscle axis hypothesis
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