Getting Enough Iron on a Plant Based Diet
Iron is everywhere on earth - its the 4th most abundant element in the earth's crust. Unfortunately, it's estimated that iron deficiency affects ~1.5-2 billion people. Now there are many complex reasons contributing to such a high rate of iron deficiency and anaemia, including poverty and food insecurity. But today I'm going to cover the ins and outs of ensuring adequate iron intake for those of you who follow a plant based diet.
Each day your body loses some iron through the GI tract, the skin, the airways and in sweat, equating to ~ 1 mg of absorbed iron per day. Women of childbearing age also need to compensate for additional losses each month, now this varies greatly from person to person, but it has been estimated to account for an additional 0.5 mg of iron per day. Infants, children, teens and women who are pregnant are at an increased risk of developing iron deficiency as they experience phases of rapid tissue growth.
Two main forms of iron are found in foods; haem iron and non-haem iron. Plant foods contain only non-haem iron, whereas animal products can contain both forms. Put simply Haem iron is more bioavailable to humans. Now, by no means do we need haem iron to be healthy, in fact intake of haem iron and high iron stores have been linked with several diseases - but thats a topic for another time. Rest assured though you can do just fine if you only consume foods that contain non-haem iron.
In Australia the recommended dietary intake of iron is 8 mg/day for the average adult male and 18 mg/day for adult females who have not yet gone through menopause. However, it is really important to note that you aren't necessarily what you eat - you are what you absorb.
It is estimated that in a typical western diet 14-17% of the iron consumed is bioavailable to use (meaning able to be absorbed), whereas it is likely that those following a vegetarian or vegan diet will only absorb 5-12% of the iron they consume. It is therefore recommended that those following a plant based diet consume higher amounts of iron to compensate for the lower rate of bioavailability. Interestingly many vegetarians already have a higher intake of iron than their meat eating counterparts, but it still may not be enough to meet needs, especially for women with heavy periods. A well-planned plant based diet can however provide sufficient iron to meet your needs, so lets run through the basics of what can help and hinder iron absorption.
Phytic acid is the phosphate storage form in plants and can hinder iron absorption. Grains such as barley, rye and wheat do contain an enzyme called phytase which helps degrade phytic acid, however, relying on this alone may not be enough for some. Preparation methods that may help reduce phytic acid content include:
- Sourdough preparation
- Soaking (and then discarding that water)
- Ensuring consumption of sufficient vitamin C
Polyphenols and Tannins
Polyphenol antioxidants are substances that are found in a wide range of foods and have health benefits. However, certain types of polyphenols can bind iron in the GI tract making it unavailable for absorption. Black tea polyphenols (Tannins) in particular are highly inhibiting - that's why its a really good idea to enjoy your cuppa away from meals and not straight before or after food. Herbal teas and red wine do not inhibit iron absorption as much as your black tea will but it may pay to avoid these drinks at meal times as well if you are working to increase your iron stores.
Calcium can modestly inhibit the absorption of both haem and non-haem iron regardless of whether it's from dairy products or supplements. Although calcium's effect on iron absorption is usually relatively small, it may pay to ensure you don't take calcium supplements around meal times, especially if you already have marginal iron status.
Oxalic Acid - A Special Mention.
Oxalic acid (OA) is a compound found in many plant foods, especially leafy greens like spinach, parsley and beet leaves - all of these also high in iron! So is it pointless to be consuming spinach for its iron? OA is known to hinder calcium absorption, but the science on whether it inhibits iron absorption has been mixed. In 2008 a well designed two-part study firstly compared the iron absorption between meals containing 150 g spinach (high in OA) and 150 g kale (low in OA). The scientists then followed up by giving participants 150 g of kale with a potassium oxalate drink to bump up the oxalate content of the meal. They found no statistically significant difference in iron absorption between the two meals, concluding that OA does not influence iron absorption in humans. I should note the iron absorption from spinach was slightly lower (but NOT statistically significant), most likely due to the high polyphenol and calcium content of spinach.
ENHANCING YOUR IRON INTAKE
Ascorbic Acid (Vitamin C)
Vitamin C has the ability to form soluble complexes with Iron and can reduce ferric to ferrous iron (which is needed for iron to be dissolved and absorbed by the GI tract) . If consumed in optimal amounts, vitamin C can increase iron absorption up to 12 fold. Vitamin C can also help offset the iron inhibiting effects of phytic acid, calcium and polyphenols/tannins.
Vitamin C in plant foods is plentiful, but good source include: