Most foods that affect your body's ability to absorb iron act exclusively or primarily on non-heme iron. This type of iron is present in plant foods, including nuts, seeds, legumes, soy products and green, leafy vegetables. Nutrients in foods that bind with and oxidize metals can both deplete your body's iron and reduce its ability to absorb iron. Rather than eliminate these foods from your diet, you can reduce their impact through a combination of food preparation techniques and careful dietary planning.
Phytate has the greatest potential of any nutrient to deplete your iron. This compound is present in large amounts in high-fiber, whole-grain foods and legumes. According to registered dietitian Dr. Reed Mangels and colleagues, phytate can reduce the body's ability to absorb iron by as much as 90 percent under laboratory conditions. However, many foods that contain large amounts of phytate also provide a source of iron. These include fortified breads and cereals, soy products and beans. This results in most phytate-containing foods having a negligible impact on iron absorption. However, foods such as wheat bran that contain large amounts of phytates with little iron can greatly deplete your iron.
Tannins are bitter compounds present in high concentrations in tea and red wine. Mangels and colleagues state that very high sources of tannins, such as black tea, can deplete your iron absorption by as much as 50 percent. Unlike foods that contain large amounts of phytates, most tannin-containing foods and beverages contain very little iron. These include berries; grape and apple juices; beer; and spices such as tamarind, turmeric and chilli powder. Foods that are rich in tannins and iron include nuts and smoked foods, such as smoked fish and meat.
Two minerals have the potential to deplete your body's iron: calcium and phosphorus. Foods or supplements that contain between 40 and 300 milligrams of calcium per serving have the greatest effect, according to Mangels and colleagues. Examples include milk, cottage cheese, kale, tofu, salmon and some grain products. In contrast with the iron-depleting effect of normal amounts of calcium, a very high phosphorus intake can also deplete your iron. Most good sources of phosphorus are also sources of iron, such as meat, fish, nuts and legumes. Foods that are very high in phosphorus and low in iron include garlic cloves, potatoes and carbonated beverages.
Countering Iron Depleters
Mangels and colleagues state that cooking foods somewhat reduces their phytate content, while pre-soaking them in water and discarding the water before cooking greatly reduces their phytate content. The vitamin C and citric acid content of citrus fruits improves your body's ability to absorb iron. However, these effects are only present if you eat iron sources with citrus fruits. Citrus fruits have a similar impact on tannins. For example, you can reduce the iron-depleting effects of tannins by adding lemon juice to tea. An additional way to avoid the negative impacts of all of these nutrients is to avoid pairing iron sources with calcium, phosphorus, phytate or tannin sources. Drinking milk, tea or red wine only between meals is an example of how to avoid their negative impact on your iron intake.
- University of Maryland Medical Center: Iron
- The Dietitian's Guide to Vegetarian Diets: Issues and Applications, Third Edition; Reed Mangels, Ph.D., R.D., et al.
- Food Biochemistry and Food Processing, Second Edition; Benjamin K. Simpson et al.
- Office of Dietary Supplements: Calcium
- University of Maryland Medical Center: Phosphorus
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