Animal sources of iron contain heme iron, which is more easily absorbed than plant forms. Many sources of meat and seafood will contain iron, but notable mentions include red meat in general, liver, and oysters. For example, 3 ounces of cooked oysters contain 8 milligrams of iron, or 44% of the daily value for iron.[1]
Plant sources of iron contain nonheme iron, which is less well absorbed than heme iron. Plant-based sources of iron include legumes, spinach, tofu, dark chocolate, chickpeas, and tomatoes. For example, half a cup of boiled and drained spinach contains 3 milligrams of iron, or 15% of the daily value for iron.[1] Besides consuming rich sources of vitamin C to increase absorption, consuming meat and/or seafood alongside plant sources of iron may also improve the absorption of plant iron.[2]
Overall, omnivorous diets result in improved iron bioavailability (around 18%) compared to plant-based diets (around 10%).[3]