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Diet and Immunity – Essential Nutrients

Diet and Immunity – Essential Nutrients

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What does the immune system do?

Our immune system is active throughout our body and exists to protect us from exposure to harmful external pathogens such as bacteria, viruses, fungi and parasites as well as environmental pollutants and food toxins, in essence it helps to keep us and our Diet and Immunity healthy! The immune system is continually working in the background, when we come into contact with something harmful, the immune system kicks in  in order to protect us. Having a well-functioning immune system is essential for keeping us healthy. Many factors influence our immune health such as age, genetics, vaccination history, early life events, lifestyle and infection history. Many of these are out of our control however our diet and nutrient status is one thing that we can control which can help to support being healthy. 

Micronutrients are essential for the proper functioning of our immune system (1). An unbalanced diet based on energy dense, nutrient poor convenience foods can lead to an inadequate intake of vitamins and minerals which can seriously impair our immune response. These types of foods may also lead to weight gain which itself has been associated with impaired immune function (2).  

There is no single food that can claim to boost the immune system however a diet that provides an adequate and balanced supply of nutrients such as vitamins A, C, D, E, B2, B6, and B12, folic acid, iron, selenium, and zinc is essential to support the functions of our immune system (1).

How does diet support the immune system?

Among other functions, vitamin D supports the immune cells in both our lungs and our gut (3). It is produced in our bodies through exposure to sunlight. Between October and April in the UK & Ireland our exposure to sunlight is too low to produce sufficient amounts, while it can only be found in low amounts in some foods, meal replacement products used for total diet replacement are fortified with vitamin D to ensure that you meet your requirements. If you’re not consuming the products, a 10mcg daily supplement is recommended to protect against deficiency.

As part of our defence system, our immune cells release molecules called reactive oxygen species whose role is to kill the harmful invading toxins. This increases the levels of oxidative stress in our bodies. In order to protect our own cells, tissues and organs from oxidative stress we require a generous supply of antioxidant nutrients (4). Vitamins C, E, selenium and zinc are all powerful antioxidants found naturally in the foods we eat such as fruits and vegetables (e.g., oranges, grapefruits, strawberries, bell peppers, spinach, kale and broccoli)  plant oils, nuts, seeds and avocado). These nutrients are also found in “nutritionally-complete” meal replacement products.

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The reactive oxygen species themselves require the amino acid arginine for their production, which is found in protein containing foods. 70% of our immune cells are associated with our gut and newer research has suggested that a healthy gut microbiome can support the immune system (5). Incorporating fibre in our diet can help to support a healthy gut microbiome. When following a total diet replacement, you should consider an additional fibre supplement to ensure sufficient fibre intake for your Diet and Immunity.

B vitamins such as folate found in green leafy vegetables as well as legumes and vitamin B12 which is found in animal products, support the essential biochemical reactions of the immune system. 

Vitamin A and zinc are both required for the generation of healthy immune cells which target an incoming infection. We know that a deficiency in vitamin A can encourage the spread of infectious diseases through the respiratory and digestive systems in children (6) . 

Our immune systems are most vulnerable during early life and as we age past 50 years. Therefore, a lifelong, varied and balanced diet is required to support a healthy, functioning immune system. When following a total diet replacement, you can be confident you are receiving adequate nutrition, however if you are deficient in certain nutrients, e.g. vitamin D, you may require further supplementation for your Diet and Immunity. 


1. Maggini S, Pierre A, Calder PC. Immune Function and Micronutrient Requirements Change over the Life Course. Nutrients. [Internet]. 2018 [cited 2021 Jan 15]; 10(10): 1531. Available from:

2. Milner JJ, Beck MA. The impact of obesity on the immune response to infection. Proc. Nutr Soc 2012 71(12): 298-306. Available from:

3. Aranow C. Vitamin D and the Immune System. J Investig Med [Internet]. 2011 [cited 2021 Jan 22];59(6):881–6. Available from:

4. De la Fuente M. Effects of antioxidants on immune system ageing. Eur J Clin Nutr [Internet]. 2002 Jul 30 [cited 2021 Jan 22];56(3):S5–8. Available from:

5. Zheng D, Liwinski T, Elinav E. Interaction between microbiota and immunity in health and disease [Internet]. Vol. 30, Cell Research. Springer Nature; 2020 [cited 2021 Jan 15]. p. 492–506. Available from:

6. Huang Z, Liu Y, Qi G, Brand D, Zheng S. Role of Vitamin A in the Immune System. J Clin Med [Internet]. 2018 Sep 6 [cited 2021 Jan 15];7(9):258. Available from:

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