Q: I know that calcium is a necessary mineral and one that, if properly assimilated, is useful in many pain situations. I, and many others, have been adding kale, spinach, beet greens, and chard to protein shakes, a current “thing to do.”
But I have read that kale and spinach, among other foods, contain oxalic acid and as such interferes with calcium absorption in the intestines. I have also read that casual consumption is ok. Can you talk about this in terms of whether adding kale in my morning shake inhibits all calcium absorption for the whole day or whether a little each day is ok? Thank you!
Maria Hepler, RDN, CLT: Calcium, which is an essential nutrient for strong bones, can be found in many green leafy vegetables, such as collard greens, spinach, mustard greens, kale, and Swiss chard. However, oxalic acid, an organic acid found in spinach, chard and beet greens, and moderately in kale, among other plants, binds with the calcium they supply and reduces its absorption, so in their raw form these should not be considered a good source of calcium.
Does this mean you should not add kale or other greens that contain oxalic acid to your smoothies? Not necessarily. Cooking or steaming these vegetables can significantly reduce the amount of oxalic acid present, which will help with calcium absorption (make sure to drain your greens thoroughly as the oxalates go in the water).
My suggestion would be to precook your leafy greens and store them in the freezer (in individual portions) for quick access. When you’re ready to make your smoothie, just grab a portion and throw it in! Cooked and drained, kale is also a great addition to soups, stews, and even pizza!
Other foods that will boost the calcium content in your smoothie, are unsweetened Greek yogurt (which also contains a good amount of protein), almonds, and flax seeds.
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