The key difference between heme iron and non-heme iron lies in how they are absorbed by the body.
How heme iron is absorbed in the body
Heme iron is found in hemoglobin and myoglobin in animal-based foods such as meat, fish, and poultry. It is absorbed in a highly efficient and unique way because it is taken up as an intact heme molecule through a specialized transport mechanism in the small intestine.
When we eat meat or fish, proteins in the food are broken down by stomach acid and digestive enzymes in the stomach and intestines. During this process, the heme group, which contains the iron, is released from hemoglobin or myoglobin.
Heme iron is absorbed as a whole unit. The exact transporter responsible for heme uptake has not yet been fully identified, but research suggests the presence of a specific heme transporter. This allows the body to absorb the iron without first needing to chemically reduce or convert it, making the process faster and more efficient.
Inside the intestinal cells, the heme group is broken down and the iron is released as Fe²⁺, the divalent form of iron.
The iron is then either temporarily stored in the cell or transported further into the bloodstream.
How non-heme iron is absorbed in the body
Non-heme iron, which is found in synthetic iron supplements as well as in plant-based foods such as legumes, nuts, seeds, grains, and certain vegetables, is absorbed through a completely different mechanism than heme iron.
In food, non-heme iron exists mainly as Fe³⁺, which is the dominant form in plant-based foods. However, the body can only absorb iron in the Fe²⁺ form.
For absorption to occur, Fe³⁺ must first be converted into Fe²⁺. This conversion requires sufficient stomach acid and specific enzymes. If stomach acid levels are low, this conversion may be impaired.
Once Fe²⁺ has been formed, it can be absorbed through a specific iron transporter called DMT1 in the lining of the small intestine.
After entering the intestinal cell, the iron is either temporarily stored in the cell or transported further into the bloodstream.
