Vegan Nutrition with Dina Aronson, M.S. R.D.

Dina Aronson, MS, RD is a vegan dietitian whose specialties include chronic disease prevention, vegetarian/vegan nutrition, and lifestyle management. She is the founder and director of VeganRD.com, a nutrition consulting company. Active in many vegetarian nutrition organizations, Dina was the recipient of the American Dietetic Association's Recognized Young Dietitian of the Year Award in 2002.

Is it true that a high intake of calcium prevents the absorption of iron? I've always had a low iron level since I'm vegan and I drink a lot of calcium-added soy milk. Can this be the reason?

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Actually, inhibitory effects of calcium on iron absorption is not well-established. I have found one textbook chapter from the 1980's that named calcium as an inhibitor of iron absorption, and a few studies demonstrating a short-term effect, but no formal studies that demonstrated this effect over the long term. In fact, two separate studies that investigated this claim, published in 2004 and 2005, respectively, in the American Journal of Clinical Nutrition, concluded that calcium supplementation had no effect on the absorption of non-heme (that is, plant-based) iron. (Read both studies here and here).

The main inhibitors of iron absorption in vegans are phytates, soy, and nutrients known as polyphenols.

It is difficult to accurately assess the degree to which iron absorption inhibitors affect overall iron absorption and status. Because iron deficiency is the world's leading dietary deficiency, it is useful to identify ways to overcome inhibitory effects of certain plant foods.

PHYTATES: Found mainly in whole grains and legumes, phytates are the most potent inhibitors of iron absorption. Refining grains is one way to reduce phytate; however, refining also removes iron. This is why iron-fortified refined grains are recommended for infants. Fiber and other protective nutrients are important components of whole grains, though, so refinement for the purpose of removing phytate is not recommended in general. Instead, using foods rich in vitamin C and other organic acids is recommended as a strategy to overcome the effects of phytate. In addition, soaking, sprouting, leavening, and fermenting whole grains render the iron more bioavailable by degrading the phytates.

SOY: Soy is a mainstay in many vegans' diets. Some studies have shown soy to have an inhibitory effect on iron absorption, although a few, including a study that investigated human iron absorption from soybeans, have shown soybeans to be a good source of absorbable iron, particularly for marginally iron-deficient women. Fermented soy products—tempeh, nato, and miso—have been shown to have higher iron bioavailability because the phytate is hydrolyzed during the fermentation process. Thus, increasing the variety of soy products to include such fermented products is one strategy that may help improve iron status. Another is to consume vitamin C-rich foods with meals.

POLYPHENOLS: Phenolic acids, flavonoids, and tannins are all examples of polyphenols that, when consumed in high amounts, may lead to decreased iron absorption. Tea, coffee, cocoa, red wine, and some herbal teas are common foods that are rich in polyphenols. As with phytates, some of the inhibitory effects of these polyphenols can be overcome, at least partially, by using them with enhancers of iron absorption.

Finally, iron absorption is affected by the presence of other minerals, such as zinc. With zinc, the effect goes both ways: too much zinc may inhibit iron absorption, and too much iron may inhibit zinc. Zinc-containing supplements, which give a bigger one-time dose of zinc than typical meals, have been shown to decrease iron absorption. Thus, it is recommended to avoid zinc-only supplements, at least at mealtime, if iron status is compromised.

Vitamin C and similar organic acids greatly enhance the absorption of iron. Thus, inclusion of more vitamin C-rich foods with foods containing inhibitors (e.g., orange juice with a meal of whole grains and beans) helps increase iron absorption. Other organic acids are found in fruits and vegetables and some processed foods. Malic acid, for example, is found in apples, and citric acid is often added to sauces and dressings to add or enhance a sour flavor.

Disclaimer: The advice given here is for eductional purposes only. You should not use this information to diagnose or treat a health problem or disease without consulting with a qualified health care provider.

Sources:

Cook JD, Morck TA, Lynch SR. The inhibitory effect of soy products on nonheme iron absorption in man. Am J Clin Nutr 1981;34:2622?9.

Hallberg L, Rossander L. Effect of soy protein on nonheme iron absorption in man. Am J Clin Nutr 1982;36:514?20. Morck TA, Lynch SR, Cook JD. Reduction of the soy-induced inhibition of nonheme iron absorption. Am J Clin Nutr 1982;36:219?28.

Hurrell RF, Juillerat MA, Reddy MB, Lynch SR, Dassenko SA, Cook JD. Soy protein, phytate, and iron absorption in humans. AAm J Clin Nutr 1992;56:573?8.

Hallberg L, Hulthén L. Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron. Am J Clin Nutr 2000;71:1147-60. Lynch, S. R. (1997), Interaction of Iron with Other Nutrients. Nutrition Reviews, 55: 102?110. doi: 10.1111/j.1753-4887.1997.tb06461.x See full index of questions

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