Eating to strengthen your immune system

by Julianne Taylor - Feel Fresh Nutrition
Monday , 3 August 2020 - 4 minute read
A chopping board of fruit and fish

Our extended summer of spectacular sunny days appears to be finally coming to a close. And as if the chillier weather alone wasn’t enough to signal it’s time to shore up our immune systems – switching from salads to comfort food like soups and casseroles – the massive global changes we’ve seen recently would seem to seal the deal.

Yes, we’re all in the same boat to some extent, dealing with uncertainty and adapting to a very different world. Which also makes now a great time to give some thought to how we each support our own personal wellbeing. After all, taking control and taking action is a great way to curb the anxiety and stress that inevitably comes with these troubled times.

Feeling on top of things mentally and being your best self physically will not only give you something to focus on over the next few weeks, it will also help your body to cope with the challenges that change brings. In other words, boost your immune system.

So in order to understand how important the role food plays in supporting our wellness, let’s first take a look at how our immune system protects our body.

What is the immune system?

Our bodies are constantly being bombarded by pathogens (bacteria, viruses, fungi and parasites – basically any germ that can cause a disease) looking for a warm, moist home where they can feed and replicate. Some, like the common cold, are simply inconvenient. Others, like coronavirus, can cause severe illness if they gain entry.

In order to stop these unwanted, tiny guests making a home in our body, we have 3 main layers of defences:

The first layer is our skin, a ‘wall’ or a physical barrier that pathogens cannot pass. Next come our mucous membranes - like those in your mouth, nose, gut and lungs - which secrete mucus and other components to immobilise and kill the invaders.

But even if a pathogen gets past these two barriers, the battle is not over. We then have 2 types of protective cells that work like our own personal army, continuously roaming the body on the lookout for foreign organisms.

The first is called our innate immune system which is non-specific and attacks anything foreign within minutes. The second is called our adaptive immune system, which has its own memory: these clever cells recognise a pathogen they have encountered in the past and proceed to kill it.

It can take several days for the adaptive system to learn to recognise new foreign invaders. However, once learned, it is ready to attack immediately if it sees this pathogen again. Thus the fact you only get things like measles once.

This is also why new diseases like coronavirus cause such havoc – no one has immunity, as our bodies simply haven’t encountered it in the past. Incidentally, this is also how vaccines work, by exposing the immune system to small amounts of a weakened virus so it can recognise it quickly the next time it is encountered. Quite ingenious really! But what does food have to do with any of this?

How food helps our immune system work

Unfortunately there is no one magic superfood or nutrient that will make your immune system work better. That’s because all the cells, organs, and weapons our immune cells use require adequate intakes of numerous vitamins, minerals, protein and essential fats to maintain their readiness to fight pathogens.

When the immune system is fighting an infection, it needs an ongoing supply of nutrients from our diet or body stores to kill pathogens and infected cells, as well as repair any damage inflicted on our body. So if we’re deficient in any nutrient, our immune system does not function as well as it might, and we’ll be more likely to get sick more often.

While all nutrients are needed, some are more important than others: namely Vitamins A, C, D, E, B6, B12, folate, iron, zinc, copper, magnesium, selenium, amino acids, and essential fatty acids 1,2. If that sounds a lot to keep track of, don’t worry - we’ll be telling you how to get all of these nutrients below.

Many New Zealanders are deficient in crucial nutrients.

It’s a hard fact to swallow, but one in four New Zealanders are deficient in zinc. Around 30% have insufficient vitamin D levels, and in those with darker skin, up to 60% inadequate vitamin D. In addition, over one third of males and half of females are deficient in selenium, and for vitamin A, 23% of males and 12% of females are deficient 3.

Why such levels of deficiency? Our current Western diet is comprised of large amounts of food that is extremely processed, with low levels of nutrients. These highly refined ingredients are typically white flour, sugar and highly refined oils, which are made into foods like donuts, bakery products, sugary cereals, instant noodles, deep fried foods, confectionary and soft drinks. In fact, these ultra-processed foods now make up over 40% of the New Zealand diet, and around 60% of the American diet. When we displace whole unprocessed nutrient dense foods with these, it is not surprising we have multiple nutrient deficiencies 4.

Ultra-processed foods harm our immune systems too.

A diet high in sugars and refined starches like white flour increases blood glucose, literally making our blood sweeter. Excess levels of blood glucose stop our immune cells from functioning properly, reducing their ability to kill pathogens5.

Inflammatory fats, like those found in deep fryers, also increase general inflammation in our body, which in turn affects both our ability to fight infection and contributes to excessive inflammatory response when we are infected 6.

Tip – Avoid deep-fried and processed foods. These should be occasional treats only.

How do we get optimal levels of nutrients in our diet?

Below are the food groups to concentrate on to ensure we get high levels of nutrients:

Unprocessed protein rich foods, especially seafood

Protein rich foods, especially those from animal and seafood sources, provide us with essential amino acids, Omega 3 (seafood), B vitamins (in particular B6 and B12), zinc (oysters in particular, as well as poultry and meat), selenium (seafood and brazil nuts), vitamin D (eggs, liver and fish), vitamin A retinol (milk, cheese, fish and liver), and iron (red meat).

Tip - Try centring your three main meals around a palm-sized protein source to make sure you get enough protein in your day.

Protein is made up of amino acids, which are the building blocks of the cells, antibodies and enzymes that make up our immune system7.

Zinc is especially important for protecting us against respiratory tract infections and in theory against COVID-19. Zinc inhibits viral entry into cells, and disrupts the viral life cycle, so even mild deficiency of zinc affects all of the immune system. Zinc lozenges can reduce the length of a cold by 2-4 days. Excessive zinc, however, impairs the immune response 8. So be careful and never use high dosages of any supplement. Just follow what is recommended on the bottle or by your GP.

The long chain forms of Omega 3 found in seafood improve immune function and play a role in calming down the inflammation produced when our body fights infections 9.

Tip - Consume seafood at least 3 times a week. Try some oysters, perhaps some tuna, salmon or white fish and you’re covered!

Eat the rainbow in fruit and vegetables – at least 5 serves of vegetables and 2 of fruit

Fruit, vegetables and plant foods contain polyphenols, which are anti-inflammatory and give fruit and vegetables their colour too. They also contain fibre which feeds our gut bacteria; a diverse range of bacteria enhances our immune response 9. Unprocessed plant foods provide vitamin C (when raw), folate, and beta carotene vitamin A.

Vitamin C enhances our immune response as well as reducing inflammation. Fresh, raw fruit and vegetables - not cooked - are high in vitamin C, especially capsicum, kale, spinach, broccoli, brussels sprouts, kiwifruit, guava, currants, oranges and lemons.

Tip - Aim for a mix of raw and cooked plant food, at least 3 cups a day. Cutting up raw veggies and having a dip ready for snacks is an easy way to fit in more veggies. Fill half your plate with colourful salad, fresh or frozen steamed veggies at meal times. Or add berries and spinach to your smoothie. We promise you won’t even taste it. The more colourful your food is, the better!

Whole food fats: avocado, olive oil, nuts and seeds

These foods contain vitamin E, anti-inflammatory components (especially rich in olive oil), selenium (2 Brazil nuts a day provide all your selenium), plus other minerals such as magnesium, zinc, copper and healthy fats.

Tip - Aim for a small handful of nuts and seeds each day. They make a great snack with a piece of fruit, and are wonderful in yoghurt or as a topping on salads or veggies. Or you can even add some nut butter to your smoothie - super delicious.

Vitamin D

Vitamin D is produced in our body through exposure to the sun. During summer we can make significant amounts if we expose our skin for short periods when the sun is high. However in winter our levels drop, so taking a supplement to keep levels optimal is recommended 10.

Tip – Supplement with vitamin D in the winter months, unless you are outside for a significant amount of time each day.

In conclusion, to build a strong immune system ready to defend you against any pathogen, eat a large variety of foods in their least processed forms, and arm yourself with the huge range of nutrients it requires. Most of us have a bit more time at home now, so let’s use that time to explore cooking and some new recipes.

Tip – Check out some awesome and delicious recipes here. Make it a household activity to choose 2-3 new recipes each week.

The nutritionists at Feel Fresh Nutrition are happy to create meal plans personalised for you and your family, complete with pictures, recipes, and nutritional information. Visit their website to see their reduced online pricing.


  1. Wintergerst, ES. et al. Contribution of selected vitamins and trace elements to immune function. Ann Nutr Metab. 2007;51(4):301-323. doi:10.1159/000107673
  2. Gombart, AF. et al. A review of micronutrients and the immune system–working in harmony to reduce the risk of infection. Nutrients. 2020;12(1). doi:10.3390/nu12010236
  3. Ministry_of_Health U of O and. A Focus on Nutrition: Key findings of the 2008/09 New Zealand Adult Nutrition Survey. 2011;Wellington.
  4. Martínez Steele, E. et al. The share of ultra-processed foods and the overall nutritional quality of diets in the US: Evidence from a nationally representative cross-sectional study. Popul Health Metr. 2017;15(1):1-11. doi:10.1186/s12963-017-0119-3
  5. Jafar, N. et al. The effect of short-term hyperglycemia on the innate immune system. Am J Med Sci. 2016;351(2):201-211. doi:10.1016/j.amjms.2015.11.011
  6. Myles IA. Fast food fever: Reviewing the impacts of the Western diet on immunity. Nutr J. 2014;13(1):1-17. doi:10.1186/1475-2891-13-61
  7. Li, P et al.. Amino acids and immune function. Br J Nutr. 2007;98(2):237-252. doi:10.1017/S000711450769936X
  8. Prasad, AS. Zinc: Role in immunity, oxidative stress and chronic inflammation. Curr Opin Clin Nutr Metab Care. 2009;12(6):646-652. doi:10.1097/MCO.0b013e3283312956
  9. Venter, C et al. Nutrition and the Immune System: A Complicated Tango. Nutrients. 2020;12(3). doi:10.3390/nu12030818
  10. Grant, WB et al. Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. Nutrients. 2020;12(4):988. doi:10.3390/nu12040988

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