Dietary iron comes in two forms: heme and non-heme. Your body is much better at absorbing heme sources of iron, which include meat, poultry, fish and seafood. Non-heme iron is present in plant foods, such as legumes, nuts, seeds, whole grain foods and green, leafy vegetables. In addition to your body's difficulties with absorbing it, most foods that inhibit iron absorption act on non-heme iron. However, you can easily counteract these effects by avoiding iron inhibitors and combining non-heme iron sources with foods that increase its absorption.
Phytic acid is one of the strongest inhibitors of non-heme iron absorption. This compound is present in whole-grain, high-fiber foods, nuts, seeds, legumes and soy products. Particularly high sources of phytates include sesame seeds, linseed, almonds, Brazil nuts and tofu. Despite this inhibitory effect, dietician Dr. Reed Mangels and colleagues note that phytate-containing foods are typically good sources of iron. As this increase in iron intake counteracts the decrease in iron absorption, most high-phytate foods have a negligible impact on your iron absorption.
Unlike foods that contain phytates, most tannin-containing foods are not sources of iron. As such, tannins have an almost purely negative impact on your body's ability to absorb non-heme iron. Black tea is one of the highest sources of tannins and can reduce your iron intake by as much as 50 percent. Other beverages that are high in tannins include red wine, beer, apple juice, berry juices and some herbal teas. Food sources of tannins include red beans, nuts, berries and smoked foods. In addition to these foods and beverages, numerous spices contain high amounts of tannins. These include turmeric, coriander, tamarind and chilli powder, all of which are common ingredients in Indian dishes.
Calcium and Phosphorus
Calcium has the potential to inhibit the intake of both heme and non-heme iron. Foods with between 40 and 300 milligrams of calcium per serving have the greatest inhibitory effect. These include tofu, kale, salmon, cottage cheese and milk. Phosphorus has a similar effect at very high concentrations. However, most foods that are rich in phosphorus are also excellent sources of iron. These include meat, poultry and fish. Other sources of phosphorus that are not as high in iron include dried fruits, whole grains, carbonated beverages, nuts, legumes and dairy products.
A number of foods either boost your body's ability to absorb iron or counteract the effects of iron absorption inhibitors. Despite their high phosphorus content, meat, fish and poultry contain compounds that increase your body's ability to absorb both heme and non-heme iron. Vitamin A can also boost iron absorption, but this effect typically occurs only if your vitamin A intake is low. Vitamin C is a very potent enhancer of non-heme iron absorption if taken at the same time as a source of iron. Vitamin C has dual effects: it breaks down non-heme iron into a more easily absorbed form and counters the inhibitory effects of phytates. In addition, the fruit acids in foods that are high in vitamin C enhance its effects. As such, eating whole citrus fruits, such as oranges, is a great way to enhance your body's ability to absorb iron.
- University or Maryland Medical Center: Iron
- The Dietitian's Guide to Vegetarian Diets: Issues and Applications, Third Edition; Reed Mangels et al.
- Food Biochemistry and Food Processing, Second Edition; Benjamin K. Simpson et al.
- Office of Dietary Supplements: Calcium
- University or Maryland Medical Center: Phosphorus
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