The Myth of the Nutrition Facts Label: Iron Absorption Debunked

Learn more about the intricacies of factors impacting iron absorption, from inhibition by oxalates and phytates to amounts needed in high demand periods like growth spurts and pregnancy, in order to attain daily nutritional recommendations.

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By Staff Writer
Jovan Mijailovic
Edited by Jovan Mijailovic

Published March 6, 2024.

A woman looking at a package of food.

Iron is a dietary trace mineral that our body requires. It plays an important role in the formation of healthy red blood cells, helps transport oxygen in blood and deliver it to muscles, and makes up a crucial component of our muscle tissue. [1] 

Iron deficiency is also the most common nutritional deficiency worldwide and can result in a variety of health concerns, such as fatigue and anemia, if left untreated. [2] 

Iron is vital to our body, fitness, and overall well-being. The InsideTracker team is here to help uncover some secrets behind iron absorption and how to optimize it.

Iron intake: What you see is not really what you get

Get up, grab a food item from your pantry, and look at the nutrition facts panel. At the bottom of the label, locate iron and the percent daily value of iron present in the food.

While it might seem that this would make it easy to know whether you're meeting your daily requirements for iron, it is unfortunately not quite that simple. The good news? Arming yourself with important iron insights can help you reach your iron goals!

Heme vs. nonheme iron absorbtion

In food, iron is present in two different forms: heme iron and nonheme iron.  

  • Heme iron, which is bound to hemoglobin and myoglobin, is found in meat, fish, and poultry. [3] Only foods derived from animal flesh provide heme iron (though they provide nonheme iron as well). 
  • Nonheme iron, on the other hand, is present in vegetables, grains, fortified foods, and supplements. [4]

» Are you constantly tired? Learn how to increase your ferritin levels

Nonheme iron is harder to absorb

While the exact absorption of heme iron is unknown (estimated to be around 15-35%), we know that the body more readily absorbs heme iron than nonheme iron (about 3-20%). [5] However, despite the fact that heme is better absorbed, most of the iron in our diets is derived from nonheme sources. It's, therefore, essential to understand some factors that enhance and inhibit our absorption of nonheme foods.

A bunch of different foods that are labeled in the words plant based sources of iron.

Optimizing nonheme iron absorption

Simply meal planning a bit can help ensure that you're getting the most out of your nonheme iron foods. Consider the following factors that can enhance nonheme absorption:

Meat, fish, or poultry (a.k.a. "the MFP Factor")

Pair your nonheme foods, such as veggies, grains, fortified foods, or supplements, with heme-rich foods. [6] The heme present in MFP will enhance your absorption of the nonheme iron.


Consume your non-heme foods with acidic foods. Think of foods rich in vitamin C, citric acid, or lactic acid. [7] For example, if you are making a pot of lentil soup, throw in some tomatoes or tomato sauce. The vitamin C from the tomatoes will help your body absorb the non-heme iron from the lentils. [8]

Fructose (*editor's note: this is not an excuse for a sugar-free-for-all!)

Stick to plant sources of fructose, such as honey, dried figs, grapes, apples, or pears, and eat them with nonheme foods. For instance, fresh chopped apples and honey enhance absorption and taste delicious atop a bowl of oatmeal, which provides a good source of nonheme iron in addition to numerous other benefits. [9]

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What makes nonheme iron harder to absorb

It is equally important to consider the many factors that can inhibit nonheme iron absorption. Be creative and consider how to separate your intake of nonheme foods from the following:

Phytates, fibers, and oxalates

Phytates and fiber are found in foods such as whole grains, soy, nuts, and legumes and can decrease the amount of non-heme iron absorbed from a meal. [10] It is important to note that some foods high in phytates, such as oatmeal, are still good sources of nonheme iron. [11]

It would hardly be advantageous to avoid consuming these healthy foods, but if you are eating foods high in phytates and fibers (such as spinach, beets, rhubarb, or leafy vegetables), be sure to consume foods that enhance nonheme absorption!

Spinach is an excellent nonheme iron source that is also high in phytates and fibers. Dress your greens with a homemade, orange juice-based dressing in order to enhance your nonheme absorption.

» Uncover how to take iron supplements to maximize absorption


Oxalates are common, naturally occurring food chemicals found in numerous food sources such as fruits, vegetables, nuts and seeds, grains, and black tea. [12] They may inhibit the body’s iron absorption by combining with iron to form a compound called iron oxide.

While some research suggests that certain oxalate-containing foods, such as spinach and fruits, may have minimal effect on nonheme iron absorption, there is no harm in pairing these healthy foods with nonheme-enhancing foods. [13]

Calcium and phosphorous

Calcium and phosphorous can significantly impact iron absorption. Increase the time between your calcium- and phosphorous-rich snacks (e.g., milk, yogurt, or cheese) and your nonheme foods. [14

In order to maximize the benefits of calcium-rich and iron-rich foods, consider having a glass of milk a couple of hours before or after your nonheme meal.

Tannins and polyphenols

Tannins and polyphenols are biological compounds present in tea and coffee that can have an inhibitory effect on iron absorption. [15] These compounds can bind with iron, therefore making nonheme iron insoluble.

While research suggests that certain beverages and foods rich in polyphenols, such as red wine, may not significantly reduce iron absorption, if you are iron deficient, be sure to leave a couple of hours between your nonheme iron-rich lunch and your afternoon tea. [16]

» Curious about your iron group? Understand what results mean for each biomarker

a picture of a variety of foods that include oranges, lemons, and

Excess intake of other minerals

Excess intake of other minerals can inhibit nonheme iron absorption. Just like iron, zinc, calcium, magnesium, and copper are also positively charged. This means that these minerals compete for the same binding sites as iron and may prevent it from binding and being absorbed. [17] 

If you take multivitamins, which are often high in these positively charged minerals, be sure to take them hours apart from mealtime.

Low stomach acid

Stomach acidity can greatly decrease the amount of iron absorbed in your stomach. [18] Elderly individuals often have less acidic stomachs, and frequent antacid use can affect your stomach’s iron absorption. So, don’t overdo it on the Tums!

Eggs and iron absorption

Eggs contain phosphoprotein, a compound with an iron-binding capacity that can impair iron absorption. Some studies have shown that one hardboiled egg can reduce the absorption of iron in a meal by as much as 28%. [19] To maximize iron absorption, consider having your egg as a standalone snack.

Increased iron needs?

It's essential to increase iron intake accordingly when the body has increased needs, such as during periods of rapid growth (in infants and toddlers), pregnancy, or blood loss. Also, know that your body is giving you a helping hand; when your iron stores are low, or you have increased needs, your body responds accordingly and helps amp up its absorption of iron.

Pro tip: You can help yourself further by being aware of nonheme-enhancing and inhibiting factors.

» Discover why women should pay attention to iron

From deficient to optimized

Iron deficiency is a silent epidemic that unknowingly affects millions of people worldwide. Therefore, it is crucial to use tools such as InsideTracker to monitor and modify iron levels. Click below to start monitoring and optimizing your iron levels today and get on the path to enhanced wellness!


[1] Ross, A. (2014). Modern nutrition in health and disease (11th ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.

[2] WHO. World Health Report, 2000. Geneva: World Health Organization, 2000.

[3] Dietary Guidelines for Americans, 2010. (2011, January 31). Retrieved December 11, 2014, from


[5] Roughead, Z. K. F., Zito, C. A., & Hunt, J. R. (2002). Initial uptake and absorption of nonheme iron and absorption of heme iron in humans are unaffected by the addition of calcium as cheese to a meal with high iron bioavailabilityThe American journal of clinical nutrition76(2), 419-425.

[6] Zijp, I. M., Korver, O., & Tijburg, L. B. (2000). Effect of tea and other dietary factors on iron absorptionCritical reviews in food science and nutrition40(5), 371-398.

[7] Hurrell, R., & Egli, I. (2010). Iron bioavailability and dietary reference valuesThe American journal of clinical nutrition91(5), 1461S-1467S.

[8] Brown, J. C., & Ambler, J. E. (1974). Iron‐stress response in tomato (Lycopersicon esculentum) 1. Sites of Fe reduction, absorption and transport.Physiologia Plantarum31(3), 221-224.

[9] Hallberg, L. (1987). Wheat fiber, phytates and iron absorptionScandinavian Journal of Gastroenterology22(S129), 73-79.

[10] Sandberg, A. S., & Svanberg, U. (1991). Phytate hydrolysis by phytase in cereals; effects on in vitro estimation of iron availabilityJournal of Food Science56(5), 1330-1333.

[11] Bering, S., Suchdev, S., Sjøltov, L., Berggren, A., Tetens, I., & Bukhave, K. (2006). A lactic acid-fermented oat gruel increases non-haem iron absorption from a phytate-rich meal in healthy women of childbearing ageBritish journal of nutrition96(01), 80-85.

[12] Ross, A. (2014). Modern nutrition in health and disease (11th ed.).

[13] Bonsmann, S., Walczyk, T., Renggli, S., & Hurrell, R. (2007). Oxalic acid does not influence nonhaem iron absorption in humans: A comparison of kale and spinach mealsEuropean Journal of Clinical Nutrition, 336-341.

[14] Hallberg, L. (1987). Wheat fiber, phytates and iron absorption

[15] Disler, P., Lynch, S. R., Charlton, R. W., Torrance, J. D., Bothwell, T. H., Walker, R. B., & Mayet, F. (1975). The effect of tea on iron absorptionGut,16(3), 193-200.

[16] Hallberg, L. (1987). Wheat fiber, phytates and iron absorption

[17] Cook, J. D., Reddy, M. B., & Hurrell, R. F. (1995). The effect of red and white wines on nonheme-iron absorption in humans. The American journal of clinical nutrition61(4), 800-804.

[18] Jacobs, A., & Miles, P. M. (1969). Role of gastric secretion in iron absorption.Gut10(3), 226-229.

[19] Hallberg, L. (1987). Wheat fiber, phytates and iron absorption