If you read about iron long enough, eventually you will stumble across two terms:
These terms refer to two different types of iron present in our diet. In this post, I explain what the differences are between these two forms of iron, and why it is so important to distinguish between the two.
Haem iron is the name given to a type of iron mainly found in animal products, especially animal muscle tissues. The name refers to a form of iron embedded in a chemical ring-like structure known as a porphyrin ring. Together, the iron atom and the porphyrin ring make up a molecule called ‘haem’.
Haem is found mainly in haemoglobin and myoglobin. Haemoglobin is one of the major proteins found in red blood cells, and is responsible for carrying oxygen throughout the body. Myoglobin is a similar protein, this time found in muscles, which is responsible for transporting oxygen in muscles.
Approximately 50% to 60% of the iron present in animal meats is haem iron.
Non-haem iron is the name for every other sort of iron found in our diet.
Non-haem iron is found mainly found in plants, but also in dairy (in small quantities—dairy is a poor source of iron), as well as in animal meats.
Unlike haem iron, which is embedded in a porphyrin ring, non-haem iron can form a complex with a wide variety of food components.
Why is this distinction important?
This distinction is important, as haem iron and non-haem iron are absorbed into the body through two entirely different pathways, affecting how well they are absorbed.
In general, haem iron is considered fairly well absorbed; while non-haem iron is considered poorly absorbed. In fact, people consuming mainly, or only, non-haem iron need up to 1.8 times more iron per day than someone consuming a mix of haem and non-haem iron!
The reason for this difference can be found in the intestine. Once released from food in the stomach, haem iron is very stable in the intestine and is able to be absorbed intact across the intestinal wall.
Non-haem iron, however, is a different story. Once released from food in the stomach, non-haem iron is very sensitive to both the change in pH as it moves from the stomach to the small intestine, as well as to many food components that we consumed it with. Often, non-haem iron forms a complex with these food components or other molecules, and cannot be absorbed.
As you can see, it is vitally important that we differentiate between these two forms of iron.
Gropper SS, Smith JL, Groff JL, ‘Advanced Nutrition and Human Metabolism’, 2009, 5th edn., Wadsworth, California.