Eating for Immunity

Dr Zuzana Wheeler writes about the role of wholefood in optimizing immunity

Good nutrition is critical for good immune system, which is necessary for an effective response to all sorts of different organisms that can make us sick, including viruses, such as COVID. Effective immune response also protects us from cancer by removing cells with “damaged” DNA. Research shows that poor nutrition is associated with poorer immune response and worse outcomes. On the other hand, wholefood diet has been linked with better health in general, as well as with better immune response. This is because “western diet”- rich in man-made fats, refined carbohydrates and sugars causes wide-spread inflammation, which impairs our ability to fight infections and cell damage (which can result in cancers). In addition, excess fat tissue, high blood glucose and insulin levels are also known to induce inflammation and impair our immune response by a variety of mechanisms. 

You can improve your general health, response to infections and reduce your risk of cancer by avoiding ultra-processed foods and replacing them with nutrient-rich wholefoods as the foundation of a balanced diet. There are several nutrients that are particularly important for a well-functioning immune system. The most important being vitamin C, Iron, Zinc, and fat soluble vitamins A, D and E. 

Vitamin C 

Vitamin C is found in many fruits and vegetables. It is sensitive to heat, so eating raw or minimally cooked fruits or vegetables (e.g. steamed, rather than boiled) is better. The richest sources of vitamin C are peppers, citrus fruit, kiwi fruit, strawberries, black currant, broccoli, brussels sprouts, potatoes and cabbage. Contrary to popular belief, there is vitamin C in meat. 

Iron 

Iron is important for efficient oxygen transport, as well as for fighting invaders. Best sources of iron are animal foods, such as oysters and other seafood (also rich in zinc), organ meats (liver, kidneys, etc.- Also rich in zinc) and unprocessed red meat. Some plants also provide iron, however iron originating from plants is more difficult to absorb. Good plant sources of iron are tahini (crushed sesame seeds), pulses, such as chickpeas or lentils, seeds (hemp, pumpkin and quinoa). 

There are lots of factors that affect the amount of iron your body can absorb from your diet. The most important factor is your body’s need for iron: more is absorbed when your body is short of iron, and less is absorbed when your stores are full. Tea, coffee and high dietary fibre reduce iron absorption, so it’s a good idea to have your iron-rich foods separately from these foods (at least half an hour before or after). 

Zinc

Fulfils many important functions in our body. Among many others, it is very important for proper function of our immune system and wound healing. Best sources of are oysters, red meat, poultry meat, eggs and dairy, hemp seeds, cocoa (e.g. good quality dark chocolate)- all these foods are also rich sources of iron and other important vitamins and minerals, as well as a variety of vegetables, particularly legumes(chickpeas and beans) and whole grains, which also provide fibre and other nutrients. 

Vitamin D

Vitamin D plays a crucial role in our immune response. There are two main sources of vitamin D, sunshine and food. Natural vitamin D is found in animal foods that are also rich in healthy fats, as it is a fat-soluble vitamin, meaning that fat is needed for it’s absorption in our body. Be st food-sources of vitamin D are oily fish (salmon, sardines, herring and mackerel), red meat, liver and eggs. There is some vitamin D in mushrooms and it is added to some plan-based foods, such as plan-based milks, such as almond or soy milk. 

Vitamin A 

Is a potent antioxidant and promotes immunity. Like vitamin D, it is fat-soluble, so needs to be eaten with healthy fat to be absorbed. 

Vitamin A is found only in animal foods, particularly liver, full fat milk and dairy products, and fatty fish. Plants, such spinach, sorrel, parsley and carrots provide a precursor for vitamin A, called beta-caroten, which is converted into active vitamin A in the liver, according to the body’s needs. 

Vitamin A can be toxic if taken in excess, however it is very hard to overdose on it, if you are consuming a varied and balanced diet. 

Vitamin E 

Is also a fat-soluble antioxidant and it’s known for its anti-inflammatory effects. It can be found in eggs, oily fish, nuts and seeds, as well as in some vegetables.  

Vitamin E is very sensitive to light and oxygen, so it’s best to consume vitamin E rich foods as fresh as possible or store then in a dark place (e.g. pantry), in air tight containers. 

Probiotics and prebiotics

Sauerkraut is an excellent source of vitamin C, vitamins B, probiotics and fibre.

Healthy microbiome plays an important role in supporting our immune system. You can look after your microbiome by avoiding ultra-processed foods and eating varied, wholefood diet. You can also add natural probiotics by regularly consuming natural, unsweetened yoghurt, unpasteurised kimchi or sauerkraut, tempeh, unpasteurized miso or nashi paste. Fibre from vegetables and wholegrain cereals can also be very beneficial. 

Special foods and supplements for better immunity

There are some foods, such as broccoli sprouts and other sprouts, chamomile, thyme, elederberries, garlic, turmeric, ginger, echinacea, etc., known to have antiviral, antibacterial and/  or anti-cancer properties, While there is some research showing such effects in a test tube, the evidence from human studies and real life is inconclusive. 

Research shows that supplements provide minimal advantage in preventing or fighting infections and that most of them are not worth the money you pay for them. 

Bottom line

In general, I recommend eating a varied, wholefood diet, with enough protein and healthy fats to optimise your immune system. While adding specific immune-supportive nutrients into your diet, and/ or using immune-supportive supplements can add an edge against fighting infections, they should only serve to complement your main defensive arsenal: good hygiene, proper hydration, healthy, wholefood diet, restful sleep, stress control, regular movement and lots of time outside, which provides both stress relief and vitamin D.