Oxalates, calcium, and iron: Less to worry about than you might think

Wednesday, August 5, 2009 4:41
Comments Off on Oxalates, calcium, and iron: Less to worry about than you might think

Q. I'm interested in the interrelationships among oxalic acid content, calcium absorption, and iron absorption.  Which greens are higher in oxalic acid and how does it affect calcium and iron availability.   Does cooking affect the oxalic content?

A.  Among the leafy greens, spinach and beet greens are highest in oxalic acid. Oxalic acid complexes with certain minerals, especially calcium and iron. However, in terms of human nutrition, this is not as big a deal as you might have heard.

While oxalates in foods interfere with the absorption of calcium from those foods they they don't block  the absorption of calcium from other foods.  In other words, the oxalates in spinach may bind to the calcium in spinach but they do not keep you from absorbing the calcium in the cheese or kale that might be in the same dish. Oxalates do not seem to have much effect on iron absorption in humans.

Here's another fly in the ointment: Calcium itself is said to inhibit the absorption of iron. But, again, the real world impact of this interaction has been exaggerated.  Studies show that increasing your calcium intake does not seem to affect the body's iron stores.  (If you're still worried about iron status, eating more vitamin C rich foods will improve iron absorption from vegetables and supplements.)

We don't list the oxalic acid content of foods in our nutrient database. Here's a resource for that info: http://www.ohf.org/docs/Oxalate2008.pdf.   Cooking does not reduce oxalic acid substantially.

Bottom line: Most foods containing oxalates are otherwise healthful foods and the oxalates they contain don't present a concern for most people.  Under normal circumstances, the only caveat I would have is not to rely on spinach (or rhubard, or beet greens) as your only source of calcium. And if it's your only source of iron, eat it with some vitamin C!

Both comments and pings are currently closed.