DFN's Queensland Lead Dietitian Emma Strutt APD explains why what we eat can have a profound effect on our immune systems. Article first published in Nourish Magazine.
Winter is upon us and we are spending more time indoors. This is the time when cold and flu viruses circulate and attempt to invade unsuspecting victims. What we eat – or don’t eat – can have a profound effect on our immune systems.
If you become deficient in certain micronutrients, including vitamins A, C and E as well as iron, zinc and selenium, your immune function can be impaired, increasing the likelihood of getting sick. When you eat a good variety from each of the core food groups – vegetables, fruits, whole grains and legumes, with the occasional brazil nut thrown into the mix – you should be covered on the nutrient front. While no diet should be seen as a panacea, healthy eating centred around whole plant foods can certainly help boost your immune system. My top five tips will help you further build your best immune system.
Look after your gut and it will look after you
The human microbiome is certainly a hot topic at the moment, and with good reason. Your gut microbiota is made up of trillions of microbial organisms. In fact, we have more bacteria cells in and on us than we do human cells! We now know that our gut bugs have a profound effect on overall health and immunity, and about two thirds of our immune system is distributed around our gut. To keep your microbiota happy and diverse you need to feed it the right stuff, and your gut loves fibre. Aim to eat at least 30g of fibre each day, ideally more.
Research suggests that people who have the highest intake of fruits, vegetables, whole grains and legumes also have higher bacterial gene counts, which has been associated with improved immune function as well as lower body weight, less inflammation and reduced risk for certain chronic diseases.
Research suggests that people who have the highest intake of fruits, vegetables, whole grains and legumes also have higher bacterial gene counts, which has been associated with improved immune function as well as lower body weight, less inflammation and reduced risk for certain chronic diseases. Certain types of fibre – known as prebiotics – enhance the growth of beneficial bacteria. Prebiotic foods include legumes, onion, garlic, leek, asparagus, artichoke and oats as well as cooked and cooled starches like potatoes, wholegrain pasta and rice. So pasta and potato salads are a great option, especially when paired with dressings made with whole ingredients rather than refined oils. Adding small amounts of fermented foods to your diet, such as tempeh, miso or water kefir may also help the growth of good gut bacteria, as many fermented foods naturally contain beneficial bacteria called probiotics.
Eat a rainbow every day
To really optimise your diet and enhance immunity, focus on eating a variety of foods of all colours. This helps to maximise your intake of phytochemicals, antioxidants, vitamins and minerals. The pigments that give food its beautiful, bright colours also provide us with protective components. The benefits of each colour group are all slightly different too. For example, orange vegetables such as sweet potato and carrot contain beta-carotene, which is a precursor to vitamin A that supports the immune system. Red foods like tomatoes and watermelons contain lycopene, an antioxidant that protects against cell damage. Dark green leafy vegetables, including kale, spinach and rocket are packed with folate and vitamin C, which maintain healthy cells and protect against infection. Blue and purple plants such as berries and grapes are bursting with anthocyanins, a group of antioxidants that have mild antibacterial effects. And I have to give a special mention to kiwi fruit! Gold kiwi fruit has been shown to reduce the incidence, severity and even duration of upper respiratory tract infections, sore throats and head congestion.
The pigments that give food its beautiful, bright colours also provide us with protective components.
Keep your diet low in fat
If you eat a plant-based diet centred around whole foods, your fat intake will generally be lower than that of the average person. And that’s a good thing! Intervention studies have shown lower fat diets, or those where fat is less than 30% of total calories, can increase the activity of a type of white blood cell that plays a major role in ridding the body of virally infected cells, and even tumour cells. Some fat in the diet is important. However, if you are adding fats to your meal, opt for whole foods such as olives, avocados, nuts and seeds in place of processed oils and spreads.
Include mushrooms and nutritional yeast
Mushrooms and nutritional yeast are as delicious as they are nutritious. Both fungi and yeasts contain compounds called beta glucans, which show great promise for keeping the immune system healthy. Although more robust research is needed, numerous studies have suggested that certain mushroom compounds have immuno-modulatory effects and can enhance natural killer cell activity (cells that fight infected cells). Nutritional yeast, also known as savoury yeast, can also help maintain the body’s defences against pathogens. It is similar to bakers yeast but undergoes a heating and drying process that deactivates it. Just one spoonful a day can reduce the occurrence of the common cold by about 25%. It also boosts the immune system, has an anti-inflammatory effect, helps counter the negative impact of stress on the body, and provides good amounts of B vitamins and protein. You’ll find the cheesy, nutty flavour perfect for dairy-free cooking.
The body’s stress response – commonly referred to as ‘fight or flight’ – is a natural process we undergo when our body is preparing to either confront or avoid a threat, whether perceived or real. Problems arise when this response is continually evoked by less critical, day-to-day stressors such as job, money or relationship challenges. Chronic stress can have a number of detrimental effects on your health and wellbeing, including suppression of your immune system and an increased susceptibility to colds and flu. While we can’t avoid all stress in our lives, nor should we aim to, developing healthy ways to mitigate stress is important. Relaxation techniques such as meditation and yoga can help lessen your body’s stress response, as can moderate amounts of physical activity. A healthy diet can also be of benefit by boosting our mood and thereby decreasing stress. A study involving over 12,000 Australians found a direct relationship between happiness and the amount of fruit and vegetables consumed. According to this study, to achieve optimal mood lift, the magic number of fruits and vegetables appeared to be eight or more serves per day.
A study involving over 12,000 Australians found a direct relationship between happiness and the amount of fruit and vegetables consumed.
I am often asked what plant foods are the absolute best for warding off colds and flu. And the simple answer is: the foods you are actually going to eat and enjoy! So you don’t like Brussels sprouts? You gag at the thought of grapefruit? Well, you don’t have to eat them. Just keep your diet varied and centred around whole plant foods and you’re well on your way to building a healthy immune system. Whole foods have thousands of active compounds that help your immune system protect you against infection. Focus on fuelling your body with what it needs and this will give you the best shot at keeping all your systems healthy and happy.
More about the author
Emma Strutt APD is Doctors For Nutrition's Lead Dietitan for Queensland.
Read her full bio here.