I've read a lot about IRON ABSORPTION. When I was studying Dietetics, a teacher gave us details about calcium; she told us it inhibits this process. So... I believe her but I've never looked for information (scientific studies, books) to confirm it. Some days ago, I started to read and look for this confirmation in medical books, Pubmed, dietetics books). Finally, the "post" is the result.
After examining all the information, my CONCLUSION was…
There are some substances that inhibit iron absorption and there are others that assist the process. There are also individual factors that inhibit or improve it. Besides, some iron and food features act in the same way.
So, as always, I thought: in a WELL-BALANCED DIET we have all the nutrients (minerals, vitamins, macronutrients) we need (always talking about people who have no disease!). The action of these factors that inhibit or assist iron absorption will be a tiny effect if we have this well-balanced diet and no pathologies.
I want to explain you some of these factors but, first of all, I want to show you the theory of iron metabolism. Take a look at the next diagram:
Can you see? Our body "loses" iron due to epithelium desquamation (the superficial cells of some organs renew themselves). Of course, in some live stages we lose a bigger amount of iron (pregnancy, period, child growth). You can try to eat rich iron food during these stages.
You can also see in the diagram: you need to eat 10-20 iron mg to absorb 1-2 mg.
I want to introduce a notion:
There are food which contains FERROUS IRON (that means: Fe2+) or FERRIC IRON (that means Fe3+). Fe2+ absorption is easier that Fe3+, this is because Fe2+ has affinity for a protein in our gut cells (where iron absorption takes place) which allows the process.
There is IRON being part of HEME GROUP, it's the one who forms Hemoglobin, for example. You know our red blood cells are composed of hemoglobin, don't you? So, we find this kind of iron in animal origin food (LIVER, over all. You can observe in the diagram above that we "store" this mineral in our liver. MEAT, EGGS). These foods contain Fe2+.
There is IRON being part of NON-HEME GROUP, you can guess we'll find it in vegetable or non-animal origin food (LEGUMES and NUTS, generally). This iron is Fe3+ (remember: it has to pass to Fe2+ to be absorbed, this is one of the reasons why it's more difficult to absorb!).
Fe2+ is soluble in alkali pH. As I told you, iron absorption is in our gut, where pH is alkali. This is another reason why Fe2+ is easier to absorb.
There are some substances that help this reaction: Fe3+ -- Fe2+. This means that improve iron absorption.
For example, HYDROCHLORIC ACID: our stomach secretes it. CITRIC ACID and C VITAMIN (lemons, oranges), MALIC ACID (apples, onions, carrots, lettuce) and TARTARIC ACID (grapes, overall). Be aware: vegetable foods are rich in these substances, and vegetable foods contain Fe3+ (difficult to absorb). It's interesting to notice that the effect of C vitamin depends on the amount.
There are some scientific studies about this question. You'll see links following the post.
Substances that inhibits iron absorption:
CALCIUM (links also after the "post"). But the effect will be worst in people who have disease, anemia for example. No problem if your diet is well-balanced and you are healthy.
PHYTATES: in vegetables, fiber and seeds. Phytates chelates iron (and other minerals as calcium, copper).
OXALATES: some vegetables (spinach for example) and nuts generally. They act in the same way as phytates.
Our body also regulates iron absorption according to our individual needs. I will not explain it here but if you are interested in knowing more about this mechanism, let me know, I will send you more information.
TO SUM UP...
Diet gives us HEME GROUP IRON and NON-HEME GROUP IRON.
The first one is easier to absorb because his form is Fe2+. The second one is more difficult because the iron form is Fe3+.
Animal origin foods are rich in heme group iron: LIVER, overall, MEAT, EGGS.
Non-animal origin foods are rich in non-heme group iron: LEGUMES, VEGETABLES, and NUTS in general.
There are substances that BOOST IRON ABSORPTION: C VITAMIN, CITRIC ACID, MALIC and TARTARIC ACID. You can find them, in general, in fruits and vegetables.
There are substances that INHIBIT THE PROCESS: CALCIUM (dairy products and vegetables), PHYTATES and OXALATES (legumes, nuts and vegetables).
Our body regulates this absorption according to our individual needs.
Remember: the substances that interfere in the process we are talking about can give us health troubles if our diet is not healthy or if we have anemia or another disease.
"Tricks": you can mix iron rich food and C vitamin in the same meal to try to increase the absorption. Or you can avoid mixing iron rich food with calcium rich food in the same meal.
Finally, remember that a well-balanced diet and healthy life-style is the solution. And you know “what healthy life-style” means, as everyone knows: quit smoking, no alcohol, exercise fit for purpose, drink water). A well-balanced diet will cover your individual micro (vitamins, minerals) and macronutrients (proteins, lipids and carbohydrates) needs.
I hope you enjoyed this "post"!!
“Alimentación y dietoterapia”; P. Cervera, J. Clapés, R. Rigolfas. Ed. McGraw Hill. 4ª Ed. 2004.
“Introducción a la Medicina Clínica”; F. Javier Laso. Ed. Elsevier Masson. 2ª Ed. 2010.
“Tabla de composición de alimentos”; Olga Moreiras, Ángeles Carbajal et al. Ed. Pirámide. 10ª Ed. 2006.
Scientific studies about calcium in iron absorption:
Scientific studies about C vitamin and phytates in the process: