Food for a strong immune system

Are there foods that support the immune system? Yes, here are some foods credited with boosting your body’s natural defences.

Eating well can boost your wellbeing in many ways, and supporting your immune system is just one of these.

The best thing to do for your immune system is to eat a balanced diet. That means making sure you get a good mix of all the food groups, avoid overly salty, sweet or processed foods, and eat at least ten portions of fruit and vegetables a day

Firstly, some interesting facts
Fact 1: People with more body fat tend to have a higher respiratory quotient (RQ) and tend to rely on their glucose burning (aerobic) metabolism and are, therefore,  more susceptible to being out of breath (note: hypoxia is a key symptom and cause of death COVID-19). Due to oxidative priority, your body has to burn off any excess glucose in your system before fat and we consume around 30% more oxygen when be burn carbohydrates compared to fat. 

Fact 2: While it can be argued that people in China may not have the same nutritional status (e.g. lower levels of the mineral selenium in many areas) and perhaps less access to health care compared to people in more affluent countries, it is also of note that more affluent countries have a higher risk due to higher rates of obesity and poor metabolic health. 

Fact 3: Our intake of the essential micronutrients (i.e. vitamins, minerals, essential fatty acids and amino acids) play an important role in our body mounting a healthy immune response.  Poor nutrition can lead to deficiencies in certain micronutrients that are required for immune function.

Chronic malnutrition is a significant risk factor for global morbidity and mortality. More than 800 million people are worldwide are estimated to be undernourished. While this is more prevalent in developing countries, undernutrition is also a problem in industrialised nations, especially in the elderly and obese. 

What is a healthy well-balanced diet?

As you can imagine, opinions are divided about what you should do nutritionally to support your immune system.  There are endless amounts of herbs, tonics or supplements being recommended to battle Coronavirus.  On the other end of the spectrum, you have dieticians telling you to eat a “healthy well-balanced diet”.  

While it’s always ideal to have a nutrient-dense diet that provides enough of all the essential nutrients from the food you eat, a few of the essential nutrients appear to play a special role in supporting healthy immune function (e.g. vitamin C, vitamin D, iron, selenium, zinc and omega 3). 

But simply taking high doses of isolated vitamins or minerals, without eating a healthy diet, may do nothing more than put extra load on your kidneys to excrete them. Additionally, foods have micro-nutrients that are missing in supplements.

In essence, getting your micronutrients from fresh and minimally processed food grown in microbe-rich soil within a thriving ecosystem will give you the best chance of getting the right amount in the ratios in a form that your body can use.  

In the following sections, we’ll look at:

  • how a number of nutrients support your immunity,
  • which foods contain more of them

Vitamin C

Vitamin C is an essential nutrient because humans (along with guinea pigs, fruit bats and other primates and mammals) can’t make their own.  It is thought that humans lost their ability to make Vitamin C because it was plentiful in our traditional diets.

Vitamin C protects your cells against reactive oxygen species that are generated by immune cells to kill pathogens.  Vitamin C also contributes to your immune defence by supporting various cellular functions of your immune system.   

Synergistic nutrients
Vitamin C works synergically with vitamins A, B5, B6, B12, E calcium, copper, folate, iron, lysine, magnesium, magnesium, methionine, phosphorus and zinc.  Hence, it’s ideal to get your vitamin C from foods that contain a full spectrum of micronutrients.

Foods that contain vitamin C (along with other synergistic nutrients in the form that your body knows what to do with) appear to be beneficial, but relying on supplements alone is not ideal.  

Losses
Losses of vitamin C during processing can range from 10% to 90%.  
Vitamin C is highly unstable and degrades in response to heat, light and alkalinity.  
That’s why it makes sense to focus on getting your vitamin C from fresh and minimally processed food.   

Vitamin C rich foods

  • kale  
  • broccoli  
  • parsley
  • sauerkraut
  • green peppers
  • cauliflower 
  • lemon juice
  • cabbage
  • kiwifruit 
  • lime juice
  • oranges
  • courgettes
  • raspberries 
  • asparagus 
  • lettuce
  • sweet potato  
  • garlic
  • cucumber
  • onion
  • blueberries

Vitamin D

Vitamin D is an essential fat-soluble micronutrient that acts as a hormone in your body to support many vital functions and processes.   

Low vitamin D is considered a major public health concern, with 13% of the world’s population thought to be deficient.  Those who live further away from the equator are at more risk.   

Adequate vitamin D is critical to maintaining strong bones because it is critical to facilitate the absorption of both calcium and phosphorus.  

Vitamin D also together with vitamin A to support healthy immune system function.  

Vitamin D3 is a potent modulator of the immune system and helps protect against infections caused by pathogens. The UK government is currently running studies on the benefits of Vitamin D and Covid.

Synergistic nutrients
Vitamin D works synergistically with vitamins A, B3, K, boron, calcium, copper, magnesium, manganese, phosphorus, sodium and calcium.    

While vitamin D can be obtained in foods like fatty fish, your body synthesises it when exposed to the sun.  It is harder to get vitamin D from food alone without sun exposure.  

Foods that contain most vitamin D

  • spinach 
  • blackberries  
  • kale  
  • raspberries 
  •  turmeric
  • seafood 
  • mackerel
  • salmon
  • sardines
  • cinnamon
  •  tea
  • black pepper

Vitamin A

Vitamin A is a fat-soluble vitamin that is critical to support your vision, fertility and reproduction.  Vitamin A helps your heart, lungs, kidneys, and other organs work properly and plays a critical role in maintaining your immune system, preventing infection and reducing acne.  

Vitamin A supports both your innate and adaptive immunity as skin and mucosal cells of the eye and respiratory, gastrointestinal forms a barrier against infections.   You will be more vulnerable to infection if you are not getting enough vitamin A.

Synergistic nutrients
Vitamin A works synergistically with vitamins B2, B3, B12, C, D, E, magnesium, selenium, manganese, potassium, phosphorus, iodine, tyrosine and zinc.   

Bioavailability 
It’s important to be aware that vitamin A comes in two forms:

Provitamin A, and 
Preformed vitamin A.
We obtain provitamin A plant-based foods (e.g. carrots), while preformed vitamin A is found in animal-based products and seafood.  

Most people can convert adequate amounts of provitamin vitamin A to preformed vitamin A, but only if they are getting enough in their diet.  

While rare, you can get excessive levels of preformed vitamin A from animal products such as liver.  

Foods that contain more vitamin A

  • whole egg
  • lettuce
  • kale  
  • parsley  
  • sweet potato  
  • almond milk
  • asparagus  
  • broccoli  
  • lamb liver
  • beef liver
  • chicken liver
  • parmesan cheese 
  • brie
  • milk  
  • cottage cheese  
  • seafood 
  • shrimp
  • salmon

Note:  Vegetables contain pro-vitamin A which your body converts to preformed vitamin A before use, while animal and seafood contain preformed vitamin A which does not need to be converted.

Protein

According to the World Health Organisation, more than one-third of the world’s underprivileged are affected by Protein Energy Malnutrition which can compromise the integrity of mucosal barriers, thus increasing your vulnerability to infections of the respiratory, gastrointestinal, and urinary tracts.  

Protein-energy malnutrition usually occurs together with deficiencies in essential micronutrients (especially vitamin A, vitamin B6, folate, vitamin E, zinc, iron, copper, and selenium).  Foods and meals that contain more vitamins, minerals and essential fatty acids have a higher percentage of protein.  Protein comes from eggs, meat, fish, nuts, seeds, tofu and is in lower levels in vegetables and grains.

Iron

Iron is required to mount effective immune responses to invading pathogens and a deficiency in iron will impair your immune responses.  

Heme iron vs non-heme iron
Iron in our diet comes in two forms: 

  • heme iron (from animal-based foods), and 
  • non-heme iron (from plant-based foods)

Bioavailability 
We absorb 15 to 35% of animal-based iron while you will only absorb 2% of plant-based iron.  You may be at risk of anaemia if you follow a strict vegan diet.  

However, if you are consuming a nutritious omnivorous diet you are unlikely to have significant issues with low or high iron levels unless you have digestive problems, consume a lot of grains or minimal vitamin C (all of which will affect the absorption).  

Vitamin C supplementation will increase your iron absorption.   

Ironically though, iron absorption is also negatively affected by the phytates in the grains. The form of iron used in fortification is also not ideal as it may cause constipation, feed pathogenic gut flora and contribute to oxidative stress that damages the intestines.  So it is not ideal to rely on fortified cereals for your iron.

Synergistic nutrients
Excess iron intake can affect zinc absorption and vice versa.  If your dietary ratio of iron:zinc is higher than 2:1 then your absorption of zinc will be reduced.   

Iron-rich foods

  • black pudding
  • chicken liver
  • lamb liver
  • beef liver
  • whole egg
  • ground beef  
  • parsley 
  • asparagus  
  • sauerkraut
  • lettuce
  • kale  
  • broccoli  
  • zucchini
  • cucumber
  • green peppers
  • cauliflower 
  • raspberries 
  • garlic
  • flax seeds
  • sweet potato  
  • cabbage
  • onion
  • kiwifruit 
  • blueberries
  • grapes
  • cashews
  • almonds
  • walnuts

Note: Iron from plant-based foods are less bioavailable.

Selenium

Selenium is an essential mineral that plays a significant role as an antioxidant, helps you regulate your thyroid and helps to protect you from oxidative damage.  Selenium plays an important role in your immune system by slowing the body’s over-active responses to certain aggressive forms of cancer. 

Selenium is thought to help with the prevention of some cancers, protect against heart disease, prevent cognitive decline and relieve with asthma symptoms.  

Synergistic nutrients
Selenium works synergistically with vitamins B3, C, E, cysteine, glutathione, methionine, zinc and iodine.   

Foods that contain more selenium include:

  • asparagus  
  • broccoli  
  • garlic
  • flax seeds
  • kale  
  • sauerkraut
  • cabbage
  • cauliflower 
  • lettuce
  • cucumber
  • onion
  • courgettes
  • liver
  • egg 
  • cheese  
  • milk 
  • minced beef  
  • Seafood 
  • shrimp
  • salmon
  • high fat foods
  • brazil nuts
  • bacon
  • cashews

Zinc

Zinc is an essential nutrient that is a cofactor for hundreds of enzyme reactions in the human body (similar to magnesium) and is critical for optimal function of the cells that control your immunity. Even marginal zinc deficiency can suppress aspects of immunity. 

In addition to your immunity, zinc is critical to a wide range of bodily functions, including reproduction, skin health and vision.   Older people are particularly at risk for zinc deficiency due to inadequate dietary zinc intake.  Plasma zinc levels also decline with age.

Bioavailability 
Soaking and sprouting beans, seeds and grains may improve zinc bioavailability.  

What interferes with zinc absorption?
Absorption of zinc is impacted by excess sugar, insufficient stomach acid, gut inflammation and allergies. Excess calcium intake impairs zinc absorption as does excess phytates (found in grains and legumes).  

Iron and zinc compete for absorption pathways, so excess iron supplementation or a high intake of foods fortified with iron can negatively impact the absorption of zinc.  

Absorption from animal sources of zinc is much higher than from plant sources, so strict vegans should allow an additional 50% more zinc in their diet. 

Foods that contain more zinc 
Foods that contain more zinc tend to be shellfish, liver or non-starchy green vegetables as listed below.  Keep in mind here that animal-based sources of zinc will also be more bioavailable.

  • minced beef  
  • parmesan cheese 
  • milk  
  • whole egg
  • brie
  • cottage cheese  
  • seafood 
  • oyster
  • crab
  • crayfish
  • squid
  • shrimp
  • anchovy
  • parsley
  • asparagus  
  • zucchini
  • broccoli  
  • lettuce
  • cucumber
  • kale  
  • cauliflower 
  • sauerkraut

Top foods to support your immunity

Rather than focusing on individual nutrients, we can determine the foods that contain more of all of these the nutrients that are critical to your immune system.  The list of foods below has been optimised to maximise your intake of all of the nutrients highlighted in this article that have been shown to play a key role in supporting a healthy immune response.  Perhaps print the list out and stick it on your fridge to remind you to include some of these foods everyday.

Miscellanious

  • bone broth
  • turmeric 
  • oregano
  • mustard
  • paprika
  • cream of tartar
  • coconut water 
  • salsa
  • nutritional yeast
  • curry powder

Animal

  • lamb liver
  • chicken liver
  • beef liver
  • sirloin steak (fat not eaten)
  • egg white
  • whole egg
  • duck eggs
  • Seafood 
  • oysters
  • mackerel
  • tuna 
  • cod
  • mussels 
  • salmon
  • sardines
  • caviar
  • shrimp

Plants

  • bok choy 
  • spinach
  • nori
  • coriander
  • parsley
  • Swiss chard
  • watercress
  • mushrooms
  • chives
  • endive
  • bell peppers
  • asparagus
  • pumpkin
  • broccoli
  • kale
  • tomato
  • Brussels sprouts
  • cauliflower 
  • broccoli sprouts
  • zucchini
  • kimchi 
  • lettuce
  • radish
  • sauerkraut
  • daikon
  • green peppers
  • peas
  • carrot (raw)
  • spring onions
  • cabbage
  • carrots 
  • celery
  • lemon
  • rocket
  • lemon juice
  • cantaloupe melon
  • kiwifruit 
  • alfalfa sprouts

In summary

While supplements may play a role in supporting your immune function, they will be of limited value if you are not already doing everything you can to maximise the nutrient-richness of the food you eat.  

Meal ideas that optimise immune-supporting nutrients

Stracciatella recipe
Serves 4-6

1 ltr vegetable or bone stock
2 bunches of spinach (or other green leafy vegetables) 2 cloves garlic
1 tablespoon olive, coconut oil or butter
3 eggs
Sprinkling of Parmesan cheese
1 can cannellini beans
Pinch salt
Pinch pepper

In a large stockpot, bring the vegetable or chicken stock to a boil.

Clean, de-stem, and chop the green leafy vegetables of your choice. Peel two cloves of garlic. Drain and rinse the cannellini beans. 

Add two tablespoons of oil or butter to a large pan, place the whole garlic cloves in the pan, and heat for several minutes to infuse the oil. When the garlic has browned, remove and discard the garlic. Add the green vegetables to the pan, stir to combine it with the oil, and heat, covered, for 3 minutes.

When the stock has come to a boil, add the vegetables and cook for two minutes at a steady simmer.

In a liquid measuring cup or small bowl, beat 3 eggs with a fork. Grate the cheese and add to the beaten eggs. Temper the eggs by drizzling a small amount of the hot stock into the eggs while beating.

With a spoon, rapidly mix the soup broth to create a “whirl- pool” and slowly pour the egg mixture into the soup (don’t stop stirring). The eggs should immediately form into “rags”. 

Tip: Make sure that that stock is at a steady simmer before you add the eggs; if the stock is not hot enough, the eggs may incorporate into the broth instead of forming ‘rags’. 


Runny fried egg, spinach and mushroom breakfast
This breakfast combines some of the most of nutrient-dense ingredients into a versatile meal that will align with just about any goal. Mushrooms provide B5 and copper.  The spinach provides vitamins A and K, and the egg contains protein and choline.

Salmon, chicory, sauerkraut and greens
This provides a broad spectrum of micronutrients for a very high level of nutrient density. The salmon provides  protein and omega 3, vitamins B3, B5, B6, B12, phosphorus, potassium and selenium.  The greens supply folate, vitamin A and vitamin K while the sauerkraut adds some vitamin C and prebiotics.

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