Eat for

       Immunity

      The purpose of this chapter on immunity is to get you thinking about immune health in a different way. Rather than thinking of immunity as an isolated system that requires ‘boosting’ with individual ingredients, think about it from the perspective of making healthy lifestyle choices to build your metabolic and energy reserve. This strengthens all of the specialised cells and organs needed to support your body’s natural immunity and homeostatic mechanisms.

      Your immune system is a collection of proteins, organs and parts of the body that work in unison to protect us from harm. This includes everything from the acid found in your stomach to prevent harmful bacteria invading your gut, to the thick protective protein layer of your skin that physically keeps harmful microbes out. Immunity also includes the complex network of specialised cells that work in superb coordinated sequences to maintain the harmony of your internal ecosystem.

      We need a resilient immune system to protect us from infective organisms like viruses and bacteria, but we also rely on this complex network to protect us from the malfunctioning of our own cells. Immunity is traditionally thought to be just our defence system, protecting us from harmful microbes that live in the external atmosphere, but it also ensures the correct functioning of our internal environment. Our immune system is responsible for identifying and appropriately clearing away mutated or malfunctioning cells that can lead to, for example, inflammation and uncontrolled growths that can become tumours.

      Trillions of times a second, chemical reactions are occurring in your body and as a product of normal metabolism and sheer probability, some cells are created that are malfunctioning or damaged.^{126, 127} In addition, normal radiation from the sun or environmental pollution from smoke inhalation can also damage your skin and lung cells respectively and this needs to be dealt with. We rely on our body to clear these damaged cells effectively, so they don’t lead to further negative effects. This is the job of our wonderful immune system. It is what we depend on to carry out these processes and it does so with beautiful precision and efficiency without us having to think about it.

      The wonderful thing about our immune system is that it is everywhere. You might think of our detoxification system as our liver and kidneys, or our mental activity centre as our brain, but our immune system has to be prepared to step into action at any site in the body. Whether it’s to protect us from a skin-cut to the leg that could be an entry point for bacteria invading the bloodstream, or recognising a malfunctioning cell in an organ and clearing it away so it doesn’t develop into a growth, your immune system is ready.

      I hope this gives you a broad idea of the magnitude of immunity and why simply eating or medicating ‘to boost’ it is a misnomer. I appreciate it’s a nice idea and an easy-to-understand concept; you eat something, it ‘boosts your immunity’ and you become a common-cold-kicking superhuman. But in reality, our bodies do not work like that. Our vast interconnected systems of cells do not simply respond to one element like Echinacea or zinc. It is called your immune system because it is an incredibly complex network of cells that require balance and harmony, and for this reason alone I hope you can already appreciate that there is no ‘silver bullet’ nutritional supplement or pharmaceutical product that magically improves your immune health.

       GUT HEALTH

      There are particular sites in the body where immune cells interact with each other and are developed, including the bone marrow, the spleen in your abdomen and lymph nodes dotted around your body such as the neck and groin. Of particular anatomical significance, however, is our gut. Our digestive system is the closest contact to the outside world. Everything we eat and drink from our environment is covered in microbes and we have been in constant communication with them in our environment throughout our evolution via this 30-foot long tube. But rather than being fearful of them, it’s important to realise that most of the microbes that live in our digestive tract are integral to our health. Our microbiota, the population of microbes including viruses and fungi but predominantly bacteria, are mostly situated in the large intestine. As we have discussed, this huge population of foreign cells is responsible for digesting food, releasing vitamins from ingredients and maintaining our health¹²⁸ (see here). The lining of the gut has to be super thin so the products of digestion and metabolites from gut microbe activity can pass through into the blood in order to be transported around the body.

      The thin gut lining facilitating transfer of nutrients is necessary, but it’s also a route for harmful microbes and products to pass into our blood which could lead to damage, therefore our immune cells need to be constantly assessing and recognising friend from foe in these areas. It is relentless work to keep our human cells in harmony with foreign microbes, as well as detecting which of these organisms we need to get rid of. This is why so many immune cells are concentrated in our digestive tract and it explains why the gut has the largest amount of ‘lymphoid tissue’ that contains cells of the immune system.¹²⁹

      So, instead of simply using the analogy of an aggressive military force to describe our immune system, I like to see our immune cells as having just as much of a peacekeeper role in the complex world that is your human body. This is because the majority of cells contained within the body don’t actually belong to us. Microbial cells outnumber our own human cells and our health, particularly our immune health, depends on us keeping this population of microbes thriving. This objective is best served with a diet and lifestyle that nurtures them.

      Having a robust and well-functioning gut population protects and bolsters our ability to deal with infections on several levels. Specific gut microbes maintain the integrity of the gut wall, preventing harmful pathogens or materials inappropriately entering the bloodstream. They secrete their own antibiotic and anti-fungal chemicals that attack harmful microbes, preventing them from colonising the gut. Beneficial microbes support an anti-inflammatory environment, which again is why good gut health improves cardiovascular disease and diabetes. The microbes themselves produce and release micronutrients that support our immune cells as well as protecting us from harmful environmental toxins.¹³⁰ Keeping our microbiota in shape improves our immune health and involves eating colourful vegetables, fibre and a wide variety of whole foods. Dishes such as the Ethiopian Berbere Curry (see here) or the Pea Orecchiette (see here) are great ways to