Non-heme iron can be harder to absorb. It's found in nuts, dried peas and beans, whole-grain breads and fortified cereals, fruits and molasses. Typically you'll manage to absorb only 4 to 5 percent of the iron in non-heme sources. In contrast, eating non-heme sources of iron together with foods containing phytates, carbonates, oxalates, phosphates or tannins will decrease absorption. Phytates are commonly found in nuts, legumes, and the germ and bran of cereal grains.
Oxalates are high in spinach, cocoa and tea.
Tea and coffee are important sources of tannins. Translated into food choices, if you're hoping to maximize the iron in your morning toast or cereal, it's better to drink orange juice than coffee or tea with your cereal. It's best to take iron supplements only under the advice of a physician or dietitian. Too much iron can be as detrimental to your health and performance as too little. A better choice is to make sure your iron reserves never dwindle by eating a variety of iron-rich foods.