The iron content of a food is a poor guide to how much iron a person actually absorbs from it. What determines the outcome is the chemical form of the iron and what else is present in the same meal.
Two forms behave very differently
Iron in meat is largely bound within haem, a ring structure that is absorbed by a dedicated pathway and is relatively unaffected by other components of the meal.
Iron in plants, eggs and dairy is non-haem, which must be in a particular chemical state to be taken up by the intestinal transporter that handles it.
Because non-haem iron depends on that conversion step, its absorption is far more variable and far more sensitive to the composition of the meal it arrives in.
Vitamin C changes the chemical state
Ascorbic acid reduces non-haem iron to the form the transporter accepts and holds it soluble as the meal moves into the less acidic small intestine.
This is why citrus, peppers or tomatoes eaten with a plant-based iron source raise absorption from that meal appreciably.
The effect is confined to the meal in which both are present, so timing matters more than daily totals in this particular case.
Tannins and phytates bind iron in place
Tea and coffee contain polyphenols that bind non-haem iron in the gut and prevent it from being absorbed.
Phytate, present in whole grains, legumes and nuts, has a similar effect and is one reason iron status can be lower on plant-based diets despite adequate intake on paper.
Soaking, sprouting and fermenting reduce phytate content, which is part of why traditional preparation methods for these foods developed as they did.
The body regulates uptake at the intestine
There is no mechanism for excreting excess iron, so control has to happen at absorption, governed by a hormone that responds to iron stores.
When stores are low, absorption rises substantially; when stores are high or inflammation is present, uptake is suppressed.
This means the same meal yields different amounts in different people and in the same person at different times, which is why intake figures alone cannot predict status.
Why iron status needs testing rather than guessing
Both deficiency and overload cause harm, and self-supplementation without testing risks the second while assuming the first.
Blood tests distinguish low stores from the low readings that inflammation can produce, and the distinction changes what should be done.
Persistent fatigue, breathlessness or unusually heavy periods are reasons to have iron status assessed by a clinician, since the cause of a deficiency matters as much as the deficiency itself.