Calcium Absorption from Greens

Based on some comments by a reader and their finding a chart of oxalate content of various greens published by the USDA (thanks, dimqua!), I decided to more rigorously document the calcium absorption from greens. What I came up with is shown in Table 5 of the (newly renamed) article on bones on VeganHealth.org, Calcium and Vitamin D.

Here is a summary of the findings:

• Studies have shown that calcium in fortified soymilk, bok choy, kale, and mustard greens is absorbed well.

• Based on oxalate levels, the calcium in turnip greens should also be absorbed well.

• Based on oxalate levels, the calcium in collards, broccoli, and watercress should be absorbed moderately well.

• Studies have shown that the calcium in spinach and rhubarb is not absorbed well.

• Based on oxalate levels, the calcium in beet greens should not be absorbed well.

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8 Responses to “Calcium Absorption from Greens”

  1. Jamie | Thrifty Veggie Mama Says:

    Does it make a difference if the greens are cooked or raw? Is the absorption the same? Can I ask what supplement(s) you take? There are so many varieties it gets overwhelming.

  2. Jack Norris RD Says:

    Jamie,

    If you look at the chart: http://veganhealth.org/articles/bones#caabsor , I put the absorption rate in the row for the food that most closely represented what they used in the study measuring absorption. In all cases, they were cooked.

    I don’t know if the calcium from raw greens is absorbed differently than cooked.

    Here is what I take for supplements:

    http://jacknorrisrd.com/?p=664

  3. Marek Says:

    Why do you suppose broccoli is better absorbed (= well) than collards (= moderately well) when broccoli has greater oxalate level (173 mg) than collards (162 mg)?

    (BTW. I’m always wondering why Americans tend to measure everything in cups. I can understand a cup of soymilk, but putting tofu or broccoli in cups? 🙂 Measuring weight rather than volume of solid food seems not just more practicle – easily done with kitchen scales – but also much more accurate.)

  4. Jack Norris RD Says:

    Sigh. I guess because I cannot read my chart correctly. I must have been looking at the calcium column instead of the oxalate column when I wrote that. I’ve moved broccoli to “moderately well” category.

  5. Jack Norris RD Says:

    Marek,

    > BTW. I’m always wondering why Americans tend to measure everything in cups.

    I think it’s probably because the dietetics profession assumes people don’t have food scales but that they do have measuring cups.

  6. Ben Says:

    As I tend to get the bulk of my calcium from three foods, I hope that’s enough (since you’ve put only one of them in the chart):

    1c steamed collards.
    2lbs steamed red cabbage.
    2lbs baked butternut squash.

    This is more or less my daily intake of these three foods, and I guess I’m getting some 250-400mg additional calcium from other foods as well.

  7. Matt Says:

    Hi Jack, thanks for this. I wonder if I could have your thoughts on three particular foods in regards to their calcium content and absorption? These are navel oranges, blackstrap molasses and chia seeds. The NLEA calcium content of a navel orange is 66mg, a tasty calcium boost. But is it easily absorbed? USDA database doesn’t cover blackstrap molasses, just regular molasses. The way I understand it, blackstrap is more refined, leaving a higher concentration of calcium. But again, do you have any thoughts on absorption? I saw that space was blank for regular molasses in the table on vegan health . org finally USDA has calcium at more than 600mg per 100g for chia seeds, but I bet you can guess the next question!
    I would be really interested and grateful for your thoughts on these jack, if you have time. Many thanks!!

  8. Jack Norris RD Says:

    Matt,

    According to this PDF from the University of Pittsburgh, oranges don’t contain more than 6 mg of oxalates per serving:

    http://www.windsorurology.co.uk/downloads/Low_Oxalate_Diet.pdf‎

    In terms of calcium absorption, that’s pretty low, so I’d assume the calcium is well-absorbed. I doubt blackstrap molasses is high in oxalates. I don’t know about chia seeds, you could try an internet search. I’m not aware of any research testing the absorption rates of any of these foods.

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