Diet + Your Immune System

Updated: Nov 26, 2020

Your immune system is designed to protect you from toxins and infections. But it can become overactive leading to inflammation, or underactive leaving you vulnerable to the flu and more serious infections. The immune system is an efficient and complex defense system.

The Immune System

The immune system has a vital role: it protects us from germs, fungi, and viruses in order to prevent or limit infection. Without an immune system, we would have no way to fight harmful things that enter our body from the outside or harmful changes that occur on the inside.

The immune system can be activated by a lot of different things that the body doesn’t recognise as its own. These are called antigens. Examples of antigens include the proteins on the surfaces of bacteria, fungi, and viruses. When these antigens attach to special receptors on the immune cells (immune system cells), a whole series of processes are triggered in the body. Once the body has come into contact with a disease-causing germ for the first time, it usually stores information about the germ and how to fight it. Then, if it comes into contact with the germ again, it recognises the germ straight away and can start fighting it faster.

Diet and your immune system

There are several steps you can take that may strengthen your immune system and not only decrease the chances that you’ll get sick in the first place, but help to reduce the intensity and shorten the duration of any cold or flu you do get. An important note to mention is to try to get your nutrients from food and be selective with supplements when you can.

Let’s look at some dietary factors that play a role in our immune health.


Increasing vitamin C intake is one of the most popular home remedies for the common cold. Sources of vitamin C are abundant and extend well beyond the ever-popular orange. Sources of vitamin C include citrus fruits, tomatoes, potatoes, strawberries, green and red bell peppers, broccoli and kiwi (1).

A high-quality study concluded that supplementing with 200 mg or more of vitamin C did not reduce the risk of catching a cold (2). However, regular vitamin C supplements had several benefits, including, reduced the symptoms of a cold, making it less severe and reducing cold duration. A supplemental dose of 1 -2 g was enough to shorten the duration of a cold (2).

The study also showed that vitamin C appears to have even stronger positive effects in people who are under intense physical stress, such as in marathon runners and skiers (2).


Zinc is crucial for the normal development and function of cells mediating innate immunity. Zinc also has the ability to function as an antioxidant, which promotes immunity (3). The best food sources of zinc come from animal origin; lamb and beef, eggs and fish (especially shellfish!). There are also some plant-based sources such as pumpkin seeds, sesame seeds, legumes, cashews, and mushrooms.


The infamous ginger. But what is the evidence for ginger and immunity? Ginger boasts many potent anti-inflammatory compounds, including a variety of antioxidants, which are substances that protect our bodies from damage (4,5). Upping your intake of antioxidant-rich foods and drinks like ginger tea may combat inflammation and keep your immune system healthy.

Plus, many common ginger drinks have ingredients such as honey and lemon juice, which may also improve immune health. For example, both honey and lemon have been shown to have antibacterial and antiviral effects (6).


The gastrointestinal tract is one of the most microbiologically active ecosystems that play a crucial role in the working of the gut immune system. Therefore, prebiotics and probiotics deserve special mention for helping prevent illness. Both are essential to gut health. And gut health is essential to immunity (7).

Prebiotics (food for our gut bacteria) help nourish our good microbiome in our gut. Usually, this is some form of semi-digestible fibre that our bacteria can eat on, and/or that helps move food through the GI tract (8).

And probiotics (the bacteria themselves) have been shown to help us recover faster, once we get sick (9).

The best whole food sources of prebiotics are:

Vegetables: asparagus, garlic, Jerusalem artichokes, leeks, and onions

Carbs: barley, beans, oats, quinoa, rye, wheat, and potatoes

Fruit: apples, bananas, berries, citrus, kiwi

Fats: flax seeds and chia seeds

The best whole food sources of probiotics are:

Dairy: yoghurt, cheese, and kefir with live and active cultures

Fermented vegetables: pickles, sauerkraut, kimchi

Fermented soy: miso, tempeh


Garlic contains compounds that help the immune system combat bacteria. Whole garlic contains a compound called alliin. When garlic is crushed or chewed, this compound turns into allicin (10). Garlic acts as an antibiotic and has consistently been found to lessen the severity of colds and other infections. Studies have shown that garlic reduces the risk of becoming sick in the first place, as well as how long you stay sick. It can also reduce the severity of symptoms (11).


Let’s go back to some old-school conventional wisdom: when you’re sick, have some chicken soup! Despite its popularity and the numerous medicinal claims, there is very little scientific research regarding bone broth. However, a few small studies have found the glycine in bone broth may have some anti-inflammatory and antioxidant effects (12).


Elderberries are loaded with antioxidants and phytonutrients. Elderberry extract has been found to reduce the length and severity of symptoms caused by the influenza virus (13). While these results are promising, further large-scale human studies are needed.

Bottom line

Nutrition is a critical determinant of immune responses, we can support its function by having a healthy balanced diet and lifestyle. A diet which includes enough energy and a good variety of fruits and vegetables may help ensure adequate intake of essential nutrients.



1) Carr AC, Maggini S. (2017). Vitamin C and Immune Function. Nutrients. 3;9(11).

2) Hemilä H1, Chalker E. (2013). Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. Jan 31;(1):CD000980.

3) Gammoh N.Z., Rink L. (2019) Zinc and the Immune System. In: Mahmoudi M., Rezaei N. (eds) Nutrition and Immunity. Springer, Cham

4) Mashhadi, N. S., Ghiasvand, R., Askari, G., Hariri, M., Darvishi, L., & Mofid, M. R. (2013). Anti-oxidative and anti-inflammatory effects of ginger in health and physical activity: review of current evidence. International journal of preventive medicine, 4(Suppl 1), S36–S42.

5) Zehsaz F, Farhangi N, Mirheidari L. The effect of Zingiber officinale R. rhizomes (ginger) on plasma pro-inflammatory cytokine levels in well-trained male endurance runners. Cent Eur J Immunol. 2014;39(2):174-80.

6) Mathai K, Anand S, Aravind A, Dinatius P, Krishnan AV, Mathai M. (2017). Antimicrobial Effect of Ginger, Garlic, Honey, and Lemon Extracts on Streptococcus mutans. J Contemp Dent Pract. 1;18(11):1004-1008.

7) Vieira Angelica, Teixeira Mauro, Martins Flaviano. (2013). The Role of Probiotics and Prebiotics in Inducing Gut Immunity. Frontiers in Immunology. 4-445.

8) Shokryazdan P1, Faseleh Jahromi M1,2, Navidshad B3, Liang JB4. (2017). Effects of prebiotics on immune system and cytokine expression. Med Microbiol Immunol. 206(1):1-9.

9) Maldonado Galdeano C, Cazorla S, I, Lemme Dumit J, M, Vélez E, Perdigón G. (2019). Beneficial Effects of Probiotic Consumption on the Immune System. Ann Nutr Metab. 74:115-124

10) Arreola, R., Quintero-Fabián, S., López-Roa, R. I., Flores-Gutiérrez, E. O., Reyes-Grajeda, J. P., Carrera-Quintanar, L., & Ortuño-Sahagún, D. (2015). Immunomodulation and anti-inflammatory effects of garlic compounds. Journal of immunology research, 2015, 401630.

11) Nantz MP1, Rowe CA, Muller CE, Creasy RA, Stanilka JM, Percival SS. (2012). Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention. Clin Nutr.31(3):337-44.

12) Zhong Z1, Wheeler MD, Li X, Froh M, Schemmer P, Yin M, Bunzendaul H, Bradford B, Lemasters JJ. (2003). L-Glycine: a novel antiinflammatory, immunomodulatory, and cytoprotective agent. Curr Opin Clin Nutr Metab Care. 6(2):229-40.

13) Porter RS1, Bode RF. (2017). A Review of the Antiviral Properties of Black Elder (Sambucus nigra L.) Products. Phytother Res. 31(4):533-554.