There are two forms of iron present in foods: heme and non-heme. I will explain what they are, how they differ and the best sources of each.
Heme iron is derived from hemoglobin, so it is only found in animal meat – red meat, poultry, and fish. Heme protein iron is mostly concentrated in the blood and muscle of animals.
Non-heme iron is found, primarily, in plants, but also in animal meat. It is not attached to any protein, which is probably for the best. I’ll explain why later.
Top Heme Iron Sources
- Beef and chicken liver
- Clams, mollusks, mussels, and oysters
- Canned sardines, in oil
Non-heme Iron Sources
- Cruciferous vegetables – red cabbage, Brussels sprouts, bok choy and broccoli
- Leafy greens – spinach, kale and collards
- Cooked beans – pinto, kidney, soybeans, black beans and adzuki beans
- Seeds – pumpkin, sesame, squash and sunflower
- Nuts – peanuts, pecans, walnuts, pistachios, cashews and almonds
- Dried fruit – seedless raisins, peaches and prunes
- Legumes – split peas and lentils
Nutritional Difference Between Heme and Non-heme Iron
Heme iron, because it is attached to a protein, is absorbed better. But the difference is not as great as one might imagine. Heme iron is typically absorbed at a rate of 7-35%. Non-heme iron is typically absorbed at a rate of 2-20%.
The absorption of non-heme iron is dependent on actual need. If your body has enough, you won’t be able to absorb much more. Heme iron absorption, on the other hand, is not dependent on deficiency/need, and this can lead to serious health issues.
“Iron encourages the formation of cancer-causing free radicals. Of course, the body needs a certain amount of iron for healthy blood cells. But beyond this rather small amount, iron becomes a dangerous substance, acting as a catalyst for the formation of free radicals. Because of this, research studies have shown that higher amounts of iron in the blood mean higher cancer risk. …
“Studies have shown that major contributors to iron excess are taking vitamin and mineral supplements that contain iron, excess consumption of red meat, and, to some extent, eating manufactured foods that have had iron added artificially. The iron present in these sources is highly absorbable. The iron in red meat, in particular, is a highly absorbable form (heme iron); however, iron from vegetarian food sources (nonheme iron) may prove to be a better choice because, while it isn’t absorbed as well as heme iron, it is sufficient to promote adequate iron levels without encouraging iron stores above the recommended range. A diet of grains, vegetables, fruits, and beans provides adequate iron, without the risk of overload.”1
This post should be considered an addendum to last week’s article, ‘Iron Deficiency and Hearing Loss’. I realized there’s no point in warning people against iron deficiency consequences without offering useful information about the foods that contain iron, and the possible consequences of consuming too much of certain sources. I hope you found this useful. And if you have any questions or comments post them below.
1 “Iron: The Double-Edged Sword”. Physicians Committee for Responsible Medicine, n.d. Web. January 2017
Greger. Michael, MD. “The Safety of Heme vs. Non-Heme Iron” Nutrition Facts, June 5, 2015, vol 25. Web. January 2017
“Iron-Rich Foods”, WebMD, n.d. Web. January 2017