Seasonal Nutrition Insights: Tips to Improve Iron Absorption

This month’s seasonal nutrition guide we take a look at the richness of iron present in vegetables grown at this time of year, and opportunities to improve iron absorption especially when our intake of iron is from plant based sources. 

What is iron and why do we need it? 

Iron (Fe) is an important nutrient that helps make haemoglobin  - a protein that transports oxygen around the body for our cells to make energy.  

We also need iron to support a healthy immune system as adequate iron stores are needed to help fight off infection.  

Low levels of iron can lead to lethargy (tiredness), paleness, bruising easily and making it hard to concentrate.  It can also mean a low immunity and resistance to illness as the ability to fight off infections and colds become weaker.   

Where do we get our iron from?

Iron (Fe) exists in two forms in foods: haem iron and non-haem iron. Foods that contain ‘haem’ iron (as well as haemoglobin) are from animal protein such as beef, poultry and fish/seafood.  Haem iron is the most bioavailable form of the two types where the body can absorb up to 40%.

Non-Haem iron on the other hand is found predominantly in plant foods (and some animal foods) and is not as well absorbed by the body as haem iron (i.e. only up to 20%).  

However, despite the fact that haem iron is better absorbed, most of the iron in our diets is derived from non haem sources.

In western populations it is estimated that we get around 85-90% of our dietary iron intake from non-haem iron sources.  These include wholegrains, nuts, seeds, legumes and fortified iron foods such as cereals (i.e. wheat-bix) and wheat flour.  It is therefore essential to understand some of the factors that enhance and inhibit our absorption of non-haem iron rich foods; especially since iron deficiency is one of the most common nutrient deficiencies in the world, affecting 30% of people worldwide, and is a particular concern among women and children.

It also doesn’t help that the nutrient value in our food has been on the decline for decades. Our land / whenua management has a critical role in increasing the levels of essential nutrients in our foods. Regenerative agricultural techniques are showing promise in lifting the nutrient profile of our food.  For instance a study found that regeneratively managed vegetables had 22% more iron and 19% more vitamin C than conventionally managed vegetables.

The good news is, we only need a relatively small amount of iron per day with the recommended iron intake range 7–18 milligrams (mg) per day for the general population and up to 27 (mg) for pregnant women. But because the bioavailability of iron from foods is complex, it’s important to understand what enhances and inhibits iron absorption in the body.

Know your potential iron enhancers

Eating haem based foods.

Because foods containing haem iron (such as meat, fish, and poultry ) make it easier for our bodies  to absorb iron more easily, did you also know that they stimulate the absorption of non-haem foods?   Having a combination of both haem iron and non-haem iron rich foods in a meal helps the body increase absorption of non-haem iron.   For example, adding lean meat to a salad sandwich increases the amount of iron absorbed from the bread and salad.

Eat foods rich in Vitamin C.

Vitamin C has nutrient star power in so many ways (if it’s not already obvious!).  It has an extraordinary ability to capture non-haem iron and store it in a form that makes it easier for the body to absorb - how cool?!  Another cool thing is that Vitamin C and Iron are present in significant amounts together in foods.  As mentioned in the Winter article, vegetables with high Vitamin C and iron include:

• Cauliflower

• Broccoli

• Parsley

• Rocket

• Cabbages (red, green, wong bok/chinese cabbage)

• Dark leafy green vegetables - spinach, kale and silverbeet

Other food sources of Vitamin C at this time of year include citrus fruits (oranges, grapefruit etc.) kiwifruit, pumpkin/squash and kūmara.  

Eat foods rich in Vitamin A - beta carotene. 

Carrots, kūmara, spinach, kale, pumpkin and squash; as well as oranges are great sources of beta carotene which converts to Vitamin A in the body. Vitamin A plays an important role in preventing iron deficiency anaemia as it helps to release iron that the body stores. Therefore, adequate vitamin A plays an important role in preventing iron deficiency.  

Eat lacto-fermented rich foods.

These show increasing promise in making non-haem iron more available to the body, in fact studies are showing iron is more readily absorbed from fermented vegetables than non-fermented ones.  

Know your potential iron inhibitors  

Some nutrient rich foods can inhibit iron absorption even though they are beneficial to overall health. These include:

Phytate or phytic acid. 

This is normally found in whole grains, cereals, soy, nuts, and legumes, and while they are important for maintaining a balanced diet, phytate is known to inhibit the absorption of non-haem iron.   Proper soaking of beans and lentils can remove phytic acid and incorporating Vitamin C rich foods and animal protein with phytate rich foods can counteract their iron inhibiting properties.  

Polyphenols (i.e. tannins). 

These are also present in a number of plant based foods including vegetables, fruits, some cereals and legumes as well as tea, coffee, and wine. Tea and coffee have a higher content of polyphenols, and while these have a number of health promoting properties, in the context of maximising iron absorption avoid drinking tea and coffee with iron rich meals.  Either drink tea and coffee between meals, or wait at least ½ -1 hour after eating.

Calcium.

To maximize absorption, calcium-rich foods should not be eaten with meals that provide most of your dietary iron (for both haem and non-haem iron rich foods). This is because calcium is a larger substance that tends to out compete iron and absorb more readily when in the present of iron in the gut.  Consuming calcium-rich foods separately from iron-rich foods can make a difference to iron absorption.

Further ideas to increase iron absorption 

Other tips for iron absorption include the benefits of cooking to increase bioavailability of non-haem iron sources. For example, the body absorbs 6% of the iron from raw broccoli, compared to 30% from cooked broccoli. 

Finally, consider cooking with iron cookware. It can add iron to your diet, particularly if you cook acidic foods at high temperatures.