You might have heard that cooking in cast-iron pans can increase the iron content of some foods. Indeed, acidic foods like tomatoes can react with the metal in a cast-iron skillet and absorb iron molecules from the pan. The greater the acidity of the food and the longer you cook it, the more iron is transferred to the food.
And foods that contain more water also seem to absorb more iron. How much iron does food absorb from cast-iron cookware? How much difference does this make in the iron content of your meal?
Potentially, a lot. Researchers cooked several foods in new cast-iron skillets and found, for example, that the amount of iron in spaghetti sauce increased from less than 1 milligram to almost 6 mg per serving. (For reference, the recommended daily intake for adult women is 18 mg per day.) Applesauce absorbed even more, going from less than half a milligram to more than 7 mg per serving. Scrambling eggs in a new iron skillet increased the iron content from 1.5 mg to almost 5 mg. But you probably won't be adding quite as much iron to your foods as the researchers in this study because they were using new pans.
Older cast-iron pans, which have become well-seasoned through use, tend to transfer less iron to food. This isn't because the iron in the pan has been used up; it's because a well-seasoned cast-iron pan has a thin coating that is formed when fat is heated to high temperatures in the pan. This coating makes the pan less reactive with the acid in foods. Cast-iron pans that are coated with enamel, by the way, will not add iron to foods.
The researchers who measured the iron levels in foods cooked in cast-iron didn't make any comment about how the foods tasted, but it's probable that the foods that absorbed the most iron also picked up a somewhat metallic taste. In a similar experiment conducted from a completely different point of view, the editors of Cook's Illustrated magazine found that cooking acidic foods in cast-iron pans—even well-seasoned ones—can impart a metallic flavor to foods if you cook them long enough. Tomatoes that were cooked for 15 minutes in a well-seasoned cast-iron skillet absorbed no off flavors, but those cooked for 30 minutes did. Foods that were either less acidic or that were cooked more briefly picked up no off flavors.
Because they're more concerned with the success of your recipes than your nutritional status, the folks at Cook's Illustrated recommend that you use stainless steel cookware when cooking acidic foods for more than a few minutes in order to reduce the chance that your dish ends up with an unpleasant metallic taste.
But even brief cooking in cast-iron can add a meaningful amount of iron to your diet.
Is cooking in cast-iron safe?
Iron deficiency is one of the most common nutrient deficiencies, especially among kids and pre-menopausal women. Pregnant women, strict vegans, those with celiac disease or a condition that causes chronic blood loss and anyone who has had gastric bypass surgery are also at increased risk. Making sure that your diet includes iron-rich foods (such as meat, seafood, beans, lentils, prunes, molasses, and fortified cereal) is probably the most straightforward way to prevent iron deficiency. But cooking in cast-iron is also a safe way to increase your iron stores. In some situations, your doctor may recommend an iron supplement as well.
On the other hand, too much iron can also cause problems. Normally, your body has fairly efficient mechanisms for getting rid of excess iron. But an inherited condition called hereditary hemochromatosis causes excess iron to build up in the body, and this can increase your risk of heart disease and certain types of cancer. The condition is actually not that uncommon—and frequently undiagnosed.
The amount of iron you'd get from a normal diet or from using cast-iron cookware is probably not going to cause a problem even if you do have this condition. But just to be on the safe side, adult men and women who have gone through menopause should avoid taking iron supplements or a multivitamin containing iron unless a doctor specifically recommends it.
Finally, don't cook dishes containing artichokes in a cast-iron pan. Phenolic compounds in artichokes react with the iron to turn these vegetables a harmless but unappetizing shade of gray!