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How can your diet support the immune system?

The immune system is a complex system that protects and defends the human body from damage from other organisms or substances from the outside environment. It is made up of a network of cells, tissues, and organs which work together to defend against pathogens. Pathogens can come in the form of viruses, or bacteria, other micro-organisms, and environmental stress and when the immune system works optimally, it neutralises the threat and removes this from the body.

One of the most vital parts of the immune system is differentiating between our own healthy cells and foreign cells or substances. The immune system is activated by antigens, which are usually proteins on the surfaces of bacteria, viruses and fungi, and this activates a cascade of cellular processes which brings varying cells of the immune system into action.

There are two parts to the immune system – the innate (non-specific) and the adaptive (specific) systems. The innate system is more like a general defence system which works against bacterial infections using killer cells. The adaptive system is a learnt defence system which deals with pathogens that the body has already learnt to defend against using anti-bodies. The two systems work together and in conjunction to defend against pathogens and harmful substances.

The immune system is a magnificent piece of human biology so understanding how the immune system works can help us understand how we can support it to work optimally. In the last 10 years, we have started to recognise that there is a solid link between eating healthily and how our immune system works through the gut microflora (the micro-organisms in our gut). These gut microflora (comprising of beneficial bacteria and others micro-organisms) are normally introduced to our gut through the process of our mothers giving birth to us. These beneficial bacteria help to mature and train our immune systems, and support the growth of a larger diversity of immune cells.

We live in symbiosis with our gut microflora and these beneficial bacteria, with our body housing the bacteria and providing food, whilst the bacteria use these resources to participate and support our health in many ways. Our diet can affect the diversity and types of bacteria fostered within our gut, and the way in which they can affect our immune system:[1]:

  • Produces short-chain fatty acids– our gut bacteria ferment dietary fibre from vegetables, fruits and wholegrains to produce short chain fatty acids (SCFA). SCFA are an important energy source for the cells of our colon along with regulating the immune process, healing, reducing inflammation and protection from cancer and other diseases.

  • Protect against pathogens– as the first line of defence, gut bacteria work by stimulating the immune response to protect against pathogenic bacteria. In addition, Lactobacilli and Bifdiobacteria can transform substances rich in fibre into lactic acid when there is no oxygen. Lactic acid acidifies our intestine and slows down proliferation of pathogenic bacteria.

  • Train our immune system– gut bacteria can selectively suppress the immune response so that we can tolerate some substances in our environment, which is important for preventing autoimmune disease and allergies. The bacterial genes can also regulate local and systemic inflammation.

Epidemiological studies have shown that eating a diet diverse in plant-based foods, including a wide range of fruits, vegetables, wholegrains, nuts, herbs, spices and seeds will help cultivate and create a balanced gut microflora which influences the balance of our immune system. We know that having a more diverse gut microflora makes us more resilient to attack from infections, pathogens, and environmental stress, which supports optimal immune health.

What should we do to support our immune system

Eat the rainbow – eat a wide range of colour

Eat one food from each colour of the rainbow each day ie blueberries for indigo, mango for yellow. Eating a diet rich in colourful vegetables and fruits ensures that you are getting a sufficient range of antioxidants. These antioxidants protect the structural elements of the immune system and the gut itself:

  • by protecting against free radical damage

  • maintain structural integrity of membranes

  • protect against DNA damage

  • support a healthy gut microflora

  • Eat a fibre-rich diet

Eating a fibre-rich diet can support the immune system protect against pathogens, and not to become hypersensitive to our diet and environment by potentially by reducing inflammatory signalling molecules[2]. Dietary fibre, both soluble and insoluble, and prebiotics such as inulin help to regulate the immune system by modifying the gut microbiome. We are advised to eat at least 30g of fibre a day but most people in the UK only eat about 18g of fibre a day. Try to eat a Mediterranean diet which is rich in wholegrains, vegetables, fruits, herbs, nuts and seeds.

Fermented foods and probiotics

Eating foods rich in beneficial bacteria such as fermented foods and probiotics (kimchi, kefir, sauerkraut, yoghurt, cheese, miso, tempeh) supports gut health by creating an environment with the right conditions for beneficial bacteria to grow in the gut. Recent research has found that humans have a receptor identifying metabolites from lactic acid bacteria (commonly found in fermented foods) which signals to the immune system mediating anti-inflammatory actions[3].

Eat oily fish and seafood

Oily fish and seafood are not only high in protein and minerals such as zinc which can help support our overall health and immune system. Oily fish such as salmon, herring and mackerel also contain essential fatty acids, DHA and EPA, which prevent disease by reducing inflammation but also by enhancing B cell activity and antibody production[i]. This mechanism might support immune system function to remove pathogens likes viruses from our bodies. Shellfish is high in zinc which has a vital role in the whole immune system[ii], particularly in the development and function of the innate immune system cells such as natural killers cells and neutrophils, and in keeping the immune system in check. Many of us are deficient in zinc so eating foods high in zinc is really important for maintaining our immune system health.

Avoid sugar and alcohol

We’ve known for a long time that drinking alcohol and eating a diet high in sugar can weaken the actions of the immune system, but we didn’t know how this might occur. Recent research has shown that alcohol is toxic to some of our immune system cells (dendritic cells), which are critical to activating the adaptive immune system via the T cells by recognising specific antigens[4]. A diet high in sugar, as shown in experiments using fruit files, abnormally activated the innate immune system causing inflammation[5]. If you are looking to enhance the activity of the immune system (and overall health), reducing both alcohol and added sugar intake in food could help.

Many of us don’t have diets or lifestyles that support optimal immune health which means that we are more prone to attack from pathogens such as cold and flu viruses. If we have other underlying conditions, this can add further stress to our immune systems, making our defences against pathogens weaker. There is no quick fix to ‘boosting’ our immune system as this could lead it to become hypersensitive or not recognise pathogens correctly. Slowly increasing the number of vegetables, fruits, herbs, nuts and seeds, wholegrains and oily fish will support your immune system in the long term.

[1] Ivanov et Honda– Intestinal microbes as immune modulators: Cell Host and

Microbe 2012;12–496-508

[2] Siracusa F, Schaltenberg N, Villablanca EJ, Huber S, Gagliani N Dietary Habits and Intestinal Immunity: From Food Intake to CD4(+) T (H) Cells. Front Immunol. 2019 Jan 15;9:3177

[3] Peters A, Krumbholz P, Jäger E, Heintz-Buschart A, Çakir MV, Rothemund S, et al. (2019) Metabolites of lactic acid bacteria present in fermented foods are highly potent agonists of human hydroxycarboxylic acid receptor 3. PLoS Genet 15(5):

[i] Gutiérrez S, Svahn SL, Johansson ME. Effects of Omega-3 Fatty Acids on Immune Cells.Int J Mol Sci. 2019 Oct 11;20(20)

Zinc as a Gatekeeper of Immune Function. Nutrients. 2017 Nov 25;9(12).

[4] A. Eken, V. Ortiz, J. R. Wands. Ethanol Inhibits Antigen Presentation by Dendritic Cells. Clinical and Vaccine Immunology, 2011; 18 (7): 115

[5] Yu S1, Zhang G1, Jin LH2. A high-sugar diet affects cellular and humoral immune responses in Drosophila.- Exp Cell Res. 2018 Jul 15;368(2):215-224.



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