Many proponents of the superiority of cast iron cookery will tell you that cooking in cast iron is a great source of iron because the iron can be leached into the food you cook, thus providing an additional source of dietary iron. And, if you cook acidic foods, such as tomato, you can get even more iron this way. They will also tell you that this iron is more readily absorbed than iron from other food sources, such as nuts, fruits, vegetables, and dairy. For example, some claim that while leafy greens are a good source of iron, they also may contain a high amount of oxalic acid, which interferes with iron absorption, thus making cast iron cooking a better source.
Importance of Iron in Nutrition
Iron is a very important mineral for our health. We need it for our red blood cells, to make hemoglobin, which transports and releases vital oxygen around our bodies. Eighty percent of the iron in our body is found in hemoglobin. But, we also need it for muscle myoglobin, and for many enzymes, essential for the function of every cell in our body. As well, iron is involved in the making of amino acids, hormones, and neurotransmitters. The human body, in fact, contains about two to four grams of iron. Men have around 50mg iron per kilogram of body weight, and women have around 38kg. And, at certain times, we need even more iron. For example, we all need more iron during times of growth, and women need more iron while pregnant.
Despite how much iron there is in our environment, we may not get nearly as much of it from our diet as we think. It has been estimated that the average American diet derives anywhere from 5 to 7mg of iron from 1000 calories (kcals) for an average diet. And, not all that iron comes in the same form.
There are two sources of iron in our diet, heme iron and non-heme iron. It is easy to remember the difference. Heme refers to the blood. So, heme iron is iron that is derived mainly from hemoglobin. Heme iron, because of the form it comes in, is readily absorbed and easily assimilated. Non-heme iron, however, tends to be bound with other food components. It has to be hydrolyzed, digested, or solubilized in the GI tract before it can be absorbed.
Cast Iron Cooking is a Good Source of Iron, But…
Nut, vegetables, fruits, grains, and cast iron skillets are all sources of non-heme iron, and thus they all have the same poor absorption, as compared to heme iron. Although cast iron is a way to get additional iron into your diet, to say that it is a superior way, without mentioning sources of heme iron, is a mistake. All sources of non-heme iron represent 70 to 90% of our iron intake. Although heme iron sources represent a very low amount of our dietary iron, their superior bio-availability means they may be responsible for up to half of the iron that is absorbed into our body.
The very best sources of dietary iron comes from liver and other organ meats. These are things we Americans do not eat much of, but they cannot be equaled as iron sources. Still, red meat is a good source too, as around 50 to 60% of the iron in red meat is heme iron. The same is true of fish and poultry.
So, if you are looking for a way to increase the iron in your diet, cooking with cast iron is one way, but you should not consider it one of the best ways. Below are the best sources of dietary iron.
In addition of these sources, be aware that many grain products, such as bread, rolls, pasta, breakfast cereals, grits, and flour, are fortified with iron, and so can represent a very good source of additional iron. In addition to simple elemental iron, these foods can use many different iron containing compounds, like ferrous ascorbate, ferrous carbonate, ferrous citrate, ferrous fumarate, ferrous gluconate, ferrous lactate, ferric ammonium citrate, ferric chloride, ferric citrate, ferric pyrophospate, and ferric sulfate. Keep in mind that the ‘best sources’ do not necessarily contain the highest amounts of iron, but the mot bio-available iron. For instance, breakfast cereals are often fortified with 100% of the daily value of iron, but this does not mean they are a better source than beef liver or red meat.
Best Sources of Iron
- Liver and other organ meats (including chicken liver)
- Red meat
- Seafood (including shellfish such as clams – oysters are an especially good source)
- Poultry (especially dark meat)
- Iron fortified foods
Also, be aware that the absorption of non-heme iron can be enhanced by the addition of certain foods. For example, consuming foods high in acids such as ascorbic acid (vitamin C), citric acid, lactic acid, or tartaric acid can increase the absorption of nonheme iron. These acids are reducing agents and form a chelate with nonheme ferric acid. For example, ascorbic acid can form ferrous ascorbate, which remains soluble in the small intestine, thus improving absorption.
Eating iron-rich vegetables along with meat, poultry, or fish can also enhance the absorption of non-heme iron, although this iron enhancing “meat-factor” is as yet unidentified. The advantage here is that these foods contain more heme iron while simultaneously enhancing the absorption of non-heme iron. Sugars, especially fructose, can help as well.
Try combining sources of nonheme iron with any of the things mentioned above. For example, when you eat your morning cereal, which is probably fortified with nonheme iron, have a glass of orange juice or eat an orange, as the vitamin C can improve the absorption of the iron.
As mentioned above, oxalic acid in leafy greens can inhibit the absorption of iron. Oxalic acid is also found in some berries, chocolate, and tea. Of course, the same factors that interfere with the absorption of non-heme iron from food, will also interfere with absorption of iron from cast iron cookware. Other factors that inhibit iron absorption are:
- Polyphenols in tea and coffee
- Phytates (phytic acid) in beans, whole grains, and corn
- Inositol hexaphosphate in beans, whole grains, and corn
- Polyphosphate in beans, whole grains, and corn
- Phosvitin in egg yolks
Despite all these factors, a varied diet with plenty of iron-containing foods will deliver the iron you need. A vegetarian diet with lots of the foods listed above, may well be deficient in iron. If you are found to have an iron deficiency, an iron supplement may be prescribed. See information on iron-deficiency anemia.