Understanding Haem and Non-Haem Iron
Iron absorption varies a lot depending on the food source. Organ meats sit at the higher end, with around 25 to 30% absorbed. Vegetables are reported at around 7 to 9%, grains at about 4%, and dried legumes at roughly 2%.
A big reason for this difference is the type of iron involved. Haem iron comes from animal foods such as red meat, poultry, and fish, and the body absorbs it more efficiently. In contrast, non-haem iron is found in plant foods such as lentils, beans, spinach, fortified cereals, and whole grains. Its absorption is much more variable and is influenced heavily by the rest of the meal.
What Can Improve Iron Absorption?
Vitamin C
Vitamin C stands out as the biggest enhancer of non-haem iron absorption. It helps convert ferric iron into the more absorbable ferrous form, which makes it more soluble in the gut.
Even adding around 50 mg of vitamin C to a plant-based meal can double iron absorption, and in some cases increase it up to sixfold. Because of that, pairing plant-based iron sources with vitamin C-rich foods can be a very useful strategy.
Cooking in Cast Iron
Cooking in cast iron can increase the iron content of food by around 15% on average. In some cases, the increase may be even greater. This seems especially relevant when cooking acidic foods, such as tomato-based sauces.
Taking Iron Supplements on an Empty Stomach
Iron supplements may work better on an empty stomach because they face less competition from compounds that reduce absorption. In the transcript, this was estimated to improve effectiveness by about 40%.
That said, there is a trade-off. Taking iron this way can increase the chance of gastrointestinal side effects. As a result, this approach may help in some cases, but it is not automatically the best option for everyone.
Including Animal Foods With Plant Sources
Combining animal foods with plant-based iron sources may slightly improve non-haem iron absorption by around 1.5 to 3%.
Although iron is often discussed as either haem or non-haem, animal foods can contain both. Even so, the broader takeaway is that mixed meals may support better overall iron absorption than plant sources alone.
What Can Reduce Iron Absorption?
Coffee and Tea
Coffee and tea can reduce iron absorption quite significantly, mainly because of their polyphenol content. Studies have shown that coffee can reduce non-haem iron absorption from a meal by about 39%, while tea reduces it by about 64%.
Importantly, timing seems to matter. Keeping coffee and tea about an hour away from meals, either before or after, appears to largely reduce this issue. Furthermore, stronger coffee may have a greater effect, so concentration may matter too.
Calcium
Calcium can also interfere with iron absorption because they compete for absorption. This applies to both haem and non-haem iron.
300 to 600 mg of calcium, which is roughly one to two cups of milk, can reduce iron absorption by around 20 to 50%. This becomes more relevant when calcium intake is very high or when calcium supplements and iron are taken together. In practice, separating them may be a sensible strategy.
Phytates
Phytates, found in foods such as whole grains, beans, and some vegetables, are another major inhibitor of non-haem iron absorption. They bind to iron and reduce how much is absorbed, reducing absorption by up to 50 to 70%.
At the same time, this does not mean these foods should be avoided. Many of these foods are still strongly associated with good health. Instead, the more helpful approach is to focus on increasing overall iron intake and improving absorption where possible, such as by including vitamin C.
A Practical Way to Think About Iron Absorption
Iron advice should be practical, not just technically correct. Some factors make a major difference, while others may matter much less than people expect.
For example, vitamin C can meaningfully improve non-haem iron absorption, while coffee, tea, calcium, and phytates can reduce it. However, context matters. Spacing coffee and tea away from meals may solve much of the issue. Separating iron and calcium can also help. Meanwhile, focusing on what can be added to meals may be more useful than becoming overly restrictive.
Final Takeaway
Iron absorption is influenced by more than just how much iron a person eats. The type of iron, the rest of the meal, and the timing of certain foods or supplements can all play a role.
Still, the goal is not to make eating feel harder. The main takeaway is to focus on the factors that make a meaningful difference, while avoiding unnecessary rules that complicate daily life without much payoff. If there are concerns about iron status, it is recommended to speak with a GP and get blood tests done.
Relevant Blog Posts
- Iron Deficiency – What You Need to Know | Ideal Nutrition
- Maximising Iron Supplementation: How to Get the Most From Your Supplements | Ideal Nutrition
- How To Get Enough Iron On A Plant-Based Diet
Relevant Studies
- Iron Absorption: Factors, Limitations, and Improvement Methods – PubMed
- Effect of dietary factors and time of day on iron absorption from oral iron supplements in iron deficient women – PubMed
- Nonheme-iron absorption from a phytate-rich meal is increased by the addition of small amounts of pork meat – PubMed
- Inhibition of food iron absorption by coffee – PubMed
- Calcium supplementation: effect on iron absorption – PubMed
- Iron absorption: no intestinal adaptation to a high-phytate diet – PubMed