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Heme iron - on top; both forms of non-heme iron below.
If you've ever experienced low iron stores and tried to raise your iron levels, you know how challenging it can be. Progress is often slow even with adequate intake. Why? Because dietary inhibitors frequently hinder iron absorption. There are two forms of iron in food:
I. Heme Iron
This form of iron is found in meat (especially high in organ meat), poultry and fish. It is stored in hemoglobin (blood) and myoglobin (muscle tissues). During digestion, these proteins break down, releasing heme iron, which is directly absorbed via its dedicated carrier protein, HCP1. Heme iron absorption is not significantly affected by other dietary components.
II. Non-Heme Iron
Found in plant-based foods, fortified foods and also animal products (approximately 40% of iron in meat), non-heme iron is typically released as Fe³⁺ (ferric iron) during digestion. To be absorbed via it's carrier DMT1, it must first be reduced to Fe²⁺ (ferrous iron) at the brush border (intestinal cell surface). This process makes non-heme iron highly sensitive to dietary factors—it can be enhanced or inhibited by other foods consumed alongside it.
Iron Absorption: Inhibitors vs. Enhancers
Iron Absorption: Inhibitors vs. Enhancers
Inhibitors reduce iron absorption by:
Competing with iron – other divalent minerals (e.g., zinc, calcium, magnesium) compete with Fe²⁺ for absorption because they share the same transporter (like a revolving door allowing only one mineral at a time).
Binding iron – they form compounds with little to no solubility that trap iron, leading to its excretion.
Enhancers increase absorption by:
Reducing iron – organic acids can convert Fe³⁺ to Fe²⁺, bypassing the need for reduction at the cell surface.
Creating soluble complexes – for example, vitamin C binds iron creating a highly soluble form that prevents inhibitor interactions and facilitates release at the intestinal cell surface.
Meat-Fish-Poultry (MFP) factor – Pairing non-heme iron with heme iron (e.g., meat, fish) boosts absorption, though the mechanism remains unclear.
Practical Tips to Maximize Iron Absorption
Practical Tips to Maximize Iron Absorption
Avoid calcium-rich foods (e.g., dairy) during iron-rich meals and 2 hours after. Also, avoid supplementation with calcium, magnesium and zinc around the same time in the day.
Pre-soak and boil legumes, grains, and nuts to reduce phytates.
Ferment, blanch, or boil vegetables to lower oxalates.
Limit coffee, tea, cocoa, red wine, and chocolate during iron-rich meals and 2 hours after.
Add organic acids (e.g., as in vinegar, citrus, tamarind puree, citrus fruits, fermented beverages) to meals.
Pair the iron rich foods with vitamin C rich products.
Combine non-heme and heme iron sources (MFP factor) when possible.
Important Note:
If you have low iron stores, consult a healthcare specialist to identify the root cause, optimal dosage, and supplement form. Excessive iron can act as a pro-oxidant—more isn’t always better.
Last updated: 14.04.2024.
For more information on the iron absorption, take a look at these books and articles:
Correnti, M., Gammella, E., Cairo, G., & Recalcati, S. (2024). Iron Absorption: Molecular and Pathophysiological Aspects. Metabolites, 14(4), 228. https://doi.org/10.3390/metabo14040228
Gropper, S. S., Smith, J. L., & Carr, T. P. (2021). Advanced nutrition and human metabolism (8th ed.). Cengage Learning.
Milman, Nils Thorm, A Review of Nutrients and Compounds, Which Promote or Inhibit Intestinal Iron Absorption: Making a Platform for Dietary Measures That Can Reduce Iron Uptake in Patients with Genetic Haemochromatosis, Journal of Nutrition and Metabolism, 2020, 7373498, 15 pages, 2020. https://doi.org/10.1155/2020/7373498
Raymond, J. L., & Morrow, K. (Eds.). (2022). Krause and Mahan's food and the nutrition care process (16th ed.). Elsevier.
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