Can healthy eating habits strengthen immunity?
Regardless of whether the world is in a pandemic situation or not, a healthy diet is good for the immune system, serving its functional needs and shaping the gut microbiota to produce an adequate immune response.
Against the current pandemic backdrop, everyone would want a stronger immune system and develop better resistance to infections. Numerous articles have highlighted the key role played by nutrition in immunity, but what can we really expect from nutrition in this regard? In fact, no study to date has shown that an improved diet can help fight viruses1,2, while protective measures and social distancing remain the most effective means of doing so. However, a well-chosen diet can optimize our immune defenses.
Two levers of action
Our food provides essential nutrients that contribute to the proper functioning of the immune system3, particularly zinc4, vitamin D5,6, vitamin A7 and antioxidants such as vitamin C5. Moreover, food affects the immune system by shaping the intestinal microbiota8,9. The billions of bacteria living in the gut are in constant dialogue with immune cells3 and play an important role in the immune response triggered by infections10 12. A well-balanced microbiota also helps regulate the immune system, preventing it from “overreacting”10,11 (i.e. maintaining a state of alert harmful to the body when it should return to standby once its mission is accomplished). For this reason, the aim is to “strengthen” rather than “boost” the immune system.
Which foods to choose?
In practice, which foods should be consumed? Fruit and vegetables–which are a source of antioxidant vitamins–, and vitamin D-rich oily fish (supplemented if possible by exposure to the sun, which favors vitamin D synthesis by the skin) provide the immune system with all its basic requirements1. In addition, a varied diet rich in fiber and probiotics such as yogurt or cheese strengthens the microbiota, promoting health and immunity14,15. Conversely, a diet too rich in calories, fats and processed foods containing additives depletes the microbiota1,8,14.
1. Physicians Committee for Responsible Medicine. Foods To Boost the Immune System. 13 March 2020. https://www.pcrm.org/news/blog/foods-boost-immune-system [last consult: 15 April 2020].
2. Harvard School of Public Health. Ask the Expert: The role of diet and nutritional supplements during COVID-19. 09 April 2020. https://www.hsph.harvard.edu/nutritionsource/2020/04/01/ask-the-expert-the-role-of-diet-and-nutritional-supplements-during-covid-19/ [last consult : 04 May 2020].
3. Childs CE, Calder PC, Miles EA. Diet and Immune Function. Nutrients. 2019 Aug; 11(8): 1933. doi: 10.3390/nu11081933.
4. Read SA, Obeid S, Ahlenstiel C, et al. The role of zinc in antiviral immunity. Advances in Nutrition. 2019 Jul 1;10(4):696-710. doi: 10.1093/advances/nmz013.
5. Ströhle A, Wolters M, Hahn A. Micronutrients at the interface between inflammation and infection--ascorbic acid and calciferol: part 1, general overview with a focus on ascorbic acid. Inflamm Allergy Drug Targets. 2011 Feb;10(1):54-63. doi: 10.2174/187152811794352105.
6. Grant WB, Lahore H, McDonnell SL, et al. Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. Nutrients. 2020 Apr 2;12(4). pii: E988. doi: 10.3390/nu12040988.
7. Huang Z, Liu Y, Qi G, et al. Role of Vitamin A in the Immune System. J Clin Med. 2018 Sep 6;7(9). pii: E258. doi: 10.3390/jcm7090258.
8. Rinninella E, Cintoni M, Raoul P et al. Food Components and Dietary Habits: Keys for a Healthy Gut Microbiota Composition. Nutrients. 2019 Oct 7;11(10). pii: E2393. doi: 10.3390/nu11102393.
9. Power SE, O'Toole PW, Stanton C, et al. Intestinal microbiota, diet and health. Br J Nutr. 2014 Feb;111(3):387-402. doi: 10.1017/S0007114513002560.
10. Hand TW. The Role of the Microbiota in Shaping Infectious Immunity. Trends Immunol. 2016 Oct;37(10):647-658. doi: 10.1016/j.it.2016.08.007.
11. Budden KF, Gellatly SL, Wood DL, et al. Emerging pathogenic links between microbiota and the gut-lung axis. Nat Rev Microbiol. 2017 Jan;15(1):55-63. doi: 10.1038/nrmicro.2016.142.
12. Belkaid Y, Hand TW. Role of the microbiota in immunity and inflammation. Cell. 2014 Mar 27;157(1):121-41. doi: 10.1016/j.cell.2014.03.011.
13. Spector T. Coronavirus: how to keep your gut microbiome healthy to fight COVID-19. The Conversation. 19 March 2020. https://theconversation.com/coronavirus-how-to-keep-your-gut-microbiome-healthy-to-fight-covid-19-134158 [last consult: 15 April 2020].
14. Zmora N, Suez J, Elinav E. You are what you eat: diet, health and the gut microbiota. Nat Rev Gastroenterol Hepatol. 2019 Jan;16(1):35-56. doi: 10.1038/s41575-018-0061-2.
15. Singh RK, Chang HW, Yan D, et al. Influence of diet on the gut microbiome and implications for human health. J Transl Med. 2017 Apr 8;15(1):73. doi: 10.1186/s12967-017-1175-y.