What are the hazards of oxalates?

Image Credit: Keith Hall/ flickr

What are the hazards of oxalates?

CC / Originally posted in How to Prevent Kidney Stones with Diet

You mention oxalates in other videos. But a vegan friend of mine has found that many of the veggies that are great sources of calcium are also high in oxalates. I understand they can affect kidney stones and the gall bladder. Any other effects? Possible subject: “How should vegans get enough calcium while avoiding oxalates”. Can they affect uric acid? Generally, “what are the hazards of oxalic acid/oxalates?” At least add both “oxalic acid” and “oxalates” to your list of topics….Thanks for whatever attention you can bring to this.


*Update: I have become concerned enough about kidney stone risk that anyone who eats cups a day (as they should!) of dark green leafy vegetables should probably stick to low-oxalate greens (i.e. basically any greens other than spinach, swiss chard, and beet greens). Video forthcoming, but just wanted to give everyone a heads up.*

Just because vegetables contain oxalates doesn’t mean they’re necessarily going to increase kidney stone risk. If anything the opposite may be true, as Dr. G points out in his video: The Downside of Green Smoothies. We do have plenty of videos on oxalates it’s just a matter of searching in the right place! I know the site can get confusing if unfamiliar, but all you have to do is click the “Health Topics” link on the top of any NutritionFacts.org page and scroll through to find what you’re looking for.  
It seems that decreasing animal protein and sodium intake is more effective in treating calcium oxalate and uric acid kidney stones than restricting calcium or oxalates. But what about preventing stones in the first place? Dr. Greger mentions the most important things we can do diet-wise is to drink 10 to 12 cups of water a day and reduce animal protein, reduce salt, and eat more vegetables and plant-based foods. See more in the video: How to Prevent Kidney Stones. (Note that the video was released after your question so I highly suggest watching it). 
Kidney stones are caused by a number of factors. Oxalates are naturally occurring compounds in many foods, vegetables in particular, that have the ability to bind to minerals like calcium and magnesium. Dr. Greger mentions more about the different types of kidney stones and ways to prevent them in: What’s the best diet for kidney stones? Interesting, vitamin C breaks down to form oxalates and large doses of vitamin C supplements is associated with greater kidney stone risk in men. Whole-food sources of vitamin C don’t seem to be a problem.

If someone already has kidney problems they should really watch their intake of turmeric (See: Who Shouldn’t Consume Curcumin or Turmeric?). Even though turmeric and cinnamon contain about the same amount of oxalates, 90% of the oxalates in turmeric are soluble (readily absorbed), which is why those with kidney problems or prone to stone formation should limit turmeric to like 1 teaspoon per day. Cinnamon isn’t a real concern oxalate-wise (but raises concerns about coumarin).

The oxalates do bind up calcium in vegetables, though, so spinach and beet greens are therefore not good sources of calcium (though wonderful foods in their own right!) Healthy sources of calcium include: kale, broccoli, collards, beans, tofu, dried figs, fortified plant-milks, and even blackstrap molasses – one of the healthiest sweeteners you can use! Calcium needs for adults 19-50 years old is 1,000 mg per day. Adults older than 50 need 1,200 mg of calcium per day, but calcium recommendations vary greatly by country. It’s like 700 mg in the U.K., which is odd , right? This huge discrepancy gives Dr. Greger the hibigeebies, meaning he questions the government panels issuing these recommendations. What does the science say? Stay tuned for clarifications in his new videos: “Are Calcium Supplements Safe?” and “Are Calcium Supplements Effective?” If you cannot wait ’till November they are available as a video download as part of his new Latest in Clinical Nutrition volume 27 (of course, all proceeds go to charity). It can also be ordered as a physical DVD. Lastly, a great cheat sheet on meeting calcium needs on a plant-based diet can be found here.

For more on diet and kidney failure watch Preventing Kidney Failure Through Diet and Treating Kidney Failure Through Diet (both summarized Dr. Greger’s blog post: Preventing and Treating Kidney Failure With Diet).

 Image Credit Keith Hall / flickr


27 responses to “What are the hazards of oxalates?

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  1. Videos on bladder issues, interstitial cystitis, frequency, etc. would be appreciated! There is a lot of unsubstantiated information online. Some claim avoiding oxalates can be helpful (a claim not backed up by research, to my knowledge), for instance. Also, people say that balancing urine pH (having it not be too acidic or too alkaline) helps and recommend avoiding most fruit. I suppose one can still consume a healthy diet low in fruit (if one emphasizes vegetables, whole grains, legumes, etc.), but aiming for neutral urine doesn’t seem like a good idea to me, at least for the long term. Videos exploring what the actual research says would be helpful! Thank you.

  2. I wish we knew more about oxalates. I checked Dr. Greger’s latest digital download #30, but I didn’t see anything in there. They need to do an oxalate content and solubility on thousands of foods just like they did with the antioxidants. My diet is pretty lacking in calcium, and I’m trying to make the proper dietary changes. I’m trying to bump up my consumption of leafy greens like kale since I’ve added turmeric and some sunflower seeds (the seeds help me reach optimal omega 6 and sodium levels) to my diet. Am I being afraid of nothing? I put everything I ate into cronometer before I switched stuff like spinach and chard for kale and it came out with ~500mg with most of the bulk coming from beans. Is that too low?

    1. Kevin: The book Becoming Vegan Express Edition (by authors recommended by Dr. Greger) is a good starting reference for figuring out individual nutrients. There is a good discussion of the various calcium issues on pages 41 and 42. On page 42, it says: “How much calcium do vegans need? It depends on how well designed the diet is and other lifestyle factors, such as physical activity. There is good evidence that intakes less than 525 mg per day increase risk.”

      The authors go on to recommend meeting the RDA, but I don’t think there is good evidence to support that. And thus I think your about 500 mg is pretty darn good. After all, “…some populations who eat less than 400 mg of calcium per day have lower rates of osteoporosis than populations who consume more than 1,000 mg per day.” (page 41)

      You may not be concerned about osteoporosis, but I’m betting you are concerned with bone health. For a really super helpful discussion of bone health and a fast read (and a book that is supported by an intensive look at more than 1,200 relevant studies), check out: “Building Bone Vitality” http://www.amazon.com/Building-Bone-Vitality-Revolutionary-Osteoporosis–Without/dp/0071600191/ref=sr_1_1_twi_pap_1?s=books&ie=UTF8&qid=1460141850&sr=1-1&keywords=building+bone+vitality I LOVE this book as it helped me to understand that bone health is way different than just worrying about calcium needs.

      1. Hey Thea it seems like you are responding to a lot of the older videos/posts, and I appreciate that. I’m still definitely going to increase it since Dr. Greger recommends at least 600mg. I was more concerned about the oxalate content reducing my total caclium intake. Do we know much how calcium is needed based on how many oxalates you are consuming? I could only find this which was helpful. http://www.childrensdayton.org/cms/resource_library/nephrology_files/5f5dec8807c77c52/lithiasis__oxalate_and_diet.pdf

        1. Kevin: I just don’t know the answer to your oxalate question for sure. I couldn’t see your link for some reason, but even if I could, I’m not qualified to interpret the validity of studies. But since you asked again, I gave it my best shot at answering you:
          As you know, Dr. Greger has some videos on the topic of oxalates, but I don’t remember those videos addressing calcium.
          And I can’t find anything about it the Becoming Vegan book. Oxalates are usually listed as potential issue around absorbing iron, not as a concern for calcium. And Becoming Vegan does list the “calcium stealers”, none of which includes oxalates as near as I can see at a glance at that section. So, the authors do look at the concept of foods that might negatively affect our calcium balance, and your concern is not included. While I may have just missed it, I’m thinking (as a complete lay person) that eating oxalates in the form of whole plant foods would not be a problem regarding calcium absorption. But I don’t know.
          FYI: I believe that most of our new medical moderators are looking at posts regardless of which page the post is on. But not all moderators are able to answer every question and NutritionFacts does not have problems with people posting “off topic” (if it’s about nutrition, it’s on topic!). So, if my answer doesn’t satisfy you and if you want to ask one of the medical moderators (I’m just a lay person), you can post your question under one of their posts or just on the latest page to see if it gets more attention. I’m just letting you know that that is acceptable. :-) But I do hope I’ve helped a little…

        2. Kevin: Wait! I want to take back part of my reply. I remember now what you are talking about. Yes, foods like spinach have high oxalates and those oxalates bind to the calcium *in* the spinach. So, this means that your body does not absorb very much of the calcium in the 3 or 4 plant foods you mention that seem to be both high in calcium and oxalates.
          However, that does not mean that a diet high in oxalates interferes in general with calcium absorption. I did hear someone ask the question once to Brenda Davis (one of the authors of Becoming Vegan), about whether say eating spinach would prevent your body from absorbing the calcium in say kale or beans. And the answer was “No”. The binding that happens is just within the plant food itself. So, for example, you could eat a spinach-kale salad and still get all the calcium from the kale that you would get if you at a kale-only salad.
          This is why oxalates are not mentioned as a general concern when it comes to calcium absorption. It is only a concern in those few plant foods, which are good for people in other areas. So, we mentioned, “Hey, don’t count on getting your calcium from say spinach or rhubarb, but those foods are also very healthy in other ways. So, eat them too for other reasons.”
          Whew. I think I got that one!

          1. Ok thank you. Would that mean that I’m actually getting less calcium than I think I am if I can’t count on something like spinach for calcium?

            1. I’m sure you probably get some calcium from spinach, but not as much as the numbers seem to show. But other plant foods are generally fine when it comes the reported calcium levels. The Becoming Vegan book has a nice big table showing a list of foods and calcium amounts. The only four plants they warn about are: spinach, swiss chard, beet greens, and rhubarb.

            2. Kevin: Some more thoughts for you: one cup of cooked collard greens is over 200 mg calcium. 1/2 cup tofu that is set with calcium is over 800 mg. 1/4 cup almonds is about 100 mg. 5 figs is about 100 mg. I picked high calcium foods from a table, but the point is: it probably wouldn’t take too much tweaking of your diet (for example, substituting cooked collards in place of the spinach) I think in order to get the calcium levels you are wanting.

            3. Here’s a tip: Go on cronometer, which uses a database of tests for nutrients in foods. Type in your day of eating – basically a general representation of what you eat. Then look at the calcium and hover over the percentage, this will tell you what percentage your spinach is contributing to your calcium sufficiency. If you’re meeting say 110% of your daily requirement and spinach is providing 10%, you’re still safe. However, if you’re getting 105% or something and spinach is still providing 10%, add another source of calcium – like some almonds or some calcium-set tofu. Cooking also destroys around 60% oxalates, but not enough to exonerate spinach.
              Almond Milk is also generally higher in calcium than other plant milks. Generally avoid Calcium Supplements, especially if you ate a really junky diet before you went vegan – unless you were raised vegan. Calcium supplements can solidify fatty plaques left over from high saturated fat meals years ago.

    2. This is a very late reply to Kevin – there is a list with oxylate levels of thousands of foods. The yahoo group Trying_Low_Oxylates has the most recent testing. For healthy people, oxylates are not a problem. I was a big spinach eater until my oxylate levels were tested and were off the chart high. I’m still able to eat healthy veggies, I just choose those with lower oxylates.

  3. I am 61 and I have osteopenia. I’ve read that some leafy greens, such as spinach (which I love eating raw in a salad) and Swiss chard are high in oxalates which can be damaging to bone density. Is this something which I should be concerned about? I hate cutting out either of these leafy greens, but I want to maintain my bone health and not develop osteoporosis. Is there a safe recommendation of how much I could eat of these on a weekly basis or should I just avoid them. Thank you for your guidance.

    1. Yogaphile: Whoever wrote that information about spinach is misinformed. Brenda Davis is a well respected RD who Dr. Greger has spoken highly of and who has even co-authored a guest post on this site. I’ve heard Brenda explain the issue with spinach, beet greens and swiss chard before. Rather than try to explain in my own words, here is what Brenda Davis says on the topic:
      “You only get about 5 percent of the calcium from spinach. Beet greens and Swiss chard are also rich in oxalates, so not great calcium sources. A lot of people ask me about collard greens. Collards are somewhere in-between the greens with excellent calcium availability and those that aren’t so great. So, although we don’t have exact figures, it is likely somewhere around 20 percent or so. This doesn’t make spinach, beet greens and Swiss chard “bad greens”. There is no such thing as bad greens unless they are poisonous. Greens are the most nutrient dense foods on the planet. Spinach may not be the best source of calcium, but it is an excellent source of folic acid! Just don’t rely on it as a calcium source.” from: http://www.choose-healthy-food.com/brenda-davis-interview-calcium-rich-foods.html
      The bottom line is that these greens are a great part of a healthy diet as they contribute to your health in a variety of ways. At the same time, these greens do not harm your bones in any way. However, you would also want to have other greens be part of your healthy diet so that you have good sources of calcium.
      If you are concerned about your bones, I highly recommend the book: “Building Bone Vitality: A Revolutionary Diet Plan to Prevent Bone Loss and Reverse Osteoporosis–Without Dairy Foods, Calcium, Estrogen, or Drugs” https://www.amazon.com/Building-Bone-Vitality-Revolutionary-Osteoporosis–Without/dp/0071600191/ref=sr_1_1_twi_pap_1?s=books&ie=UTF8&qid=1467471156&sr=1-1&keywords=building+bone+vitality The book will help you understand which foods contribute to healthy bones, put the calcium issue into perspective, and equally important, includes a chapter on which types of exercise are important. The proper exercise is vital for healthy bones. You might also want to look at the talk from Dr. Klaper on healthy bones as he gives some great advice in both diet and exercise.
      Does that help?

  4. I have a question related to calcium rates in greens.
    I know that the calcium absoption rate of kale is particularly good but unfortunalety it’s pretty much impoosible to get kale where I live (southern Austria). What about stinging nettle? Would that be a good calcium source?
    And what about cabbage? These are very easy to find …

    Any help would be highly appreciated! Thanks and best regards from Austria.

    1. Johanna Zweiger: Have you seen the NutrtionData.Self website? They don’t have *every* food of their website, but they have many foods in their database–which is really the USDA database of food nutrients. You can search for a food on their website. And then if you find the food, you can scroll down to the various nutrients, including calcium. Then you can compare calcium in various foods such as say kale and cabbage.
      Here is a food page for cabbage: http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2371/2 Scroll down to the ‘minerals’ section to see how much calcium the food has. You can control the serving size in a drop down closer to the top of the page.
      As Joseph explained in his post above, the amount of calcium in some greens are bound up in the oxalates. So, in those cases, the amount of calcium in the food is misleading. The foods that have misleading amounts of calcium are: spinach, beet greens and swiss chard. (http://www.choose-healthy-food.com/brenda-davis-interview-calcium-rich-foods.html ) So, I think you can look up other foods and generally feel pretty safe about comparing the calcium levels in those foods. (If someone else knows of additional foods to add to the list, please speak up.)
      Hope that helps.

      1. Dear Thea, that’s a really great website – thanks a lot!
        It seems that cabbage is not that great of a source for calcium with only 40 mg per 100g. They don’t have anything on stinging nettle, unfortunately. I guess I’ll keep looking for other sources then …
        Thanks again and best regards!

  5. Been looking at other vegetables for better than considered excellent sources of calcium like kale and watercress. From one study:

    Spinach, which belongs to group 1 with a ratio of 4.58 using Noonan and Savage’s (1999) criteria, now falls into the medium ratio group whereas green amaranth, purple amaranth and colocasia [taro] leaves fall into the high unavailable calcium ratio group with very high proportions of calcium bound to oxalate, ranging from 68.3% to 86.7%. In the medium unavailable calcium ratio group, the levels varied between 22.4% for shepu [dill] leaves and 40.3% for curry leaves.

    Best sources I’ve found so far are: cauliflower leaves, fenugreek leaves, moringa leaves, and possibly broccoli leaves. Still looking.

    1. Thanks! I’ll keep looking, too. My next mission is to find kale btw. Heard that you CAN get it where I live. It’s just a few places that sell it, though … I guess it’s “challenge accepted”. ;)

  6. This is a very late reply to Kevin – there is a list with oxylate levels of thousands of foods. The yahoo group Trying_Low_Oxylates has the most recent testing. For healthy people, oxylates are not a problem. I was a big spinach eater until my oxylate levels were tested and were off the chart high. I’m still able to eat healthy veggies, I just choose those with lower oxylates.

  7. I have osteoarthritis, and anything with high amounts of oxalates causes me joint pain. Pity, love spinach and Swiss chard. I still eat them, but I usually pay for it later.

    I recently purchased some calcium aspartate, calcium orotate, and magnesium orotate supplements, just to make sure I was getting enough. I can’t eat as much food on this whole foods thing (been on it almost 2 months) to get my RDA’s, as the only time I’m ever really hungry anymore is at breakfast. However, my body is really good about telling me what I’m short on, by making me crave it. First time in my life I’ve ever craved a box of silken tofu, vegetable juice, or a bunch of kale, LOL. And, oddly enough, I don’t miss meat/dairy/eggs. At all. In fact, the thought of eating it makes me slightly nauseous. Weird.

    Anyway, question is, does anyone know of any issues with these supplements? I was taking calcium carbonate and magnesium something or other, til I found out how it can cause kidney stones, and is pretty much not very bio-available. I was very unhappy to find that out. I’d been taking it for years. But the manufacturers don’t bother to tell you important stuff like that, now, do they. *snort*

    1. Adam, I am seeing lots on kidney stones, but can you recommend a video that might speak to oxalates causing dizziness or bladder irritation or ask Dr. Greger to make one.

      9 years ago I hit my head and knocked the crystals loose in my ear causing severe vertigo until they worked their way back in. Ever since, the consumption of higher oxalate foods like beans, potatoes and greens cause attacks of vertigo, which I think may be related to the oxalate crystals getting into my ears. (Although there could be another chemical pathway at work in the brain, it is still a little bit of a mystery as to why it happens, I just know that it does.) An ENT told me he had never heard of such a thing, but I’ve actually met several people since who suffer the same issue. They also commonly suffer urinary irritation after eating these food. With the switch to plant-based I am hoping this issue will resolve as nutritional imbalances correct, but it is certainly limiting and problematic in the meantime.

  8. Hi,

    This is a very interesting point, what I can offer you as a nutrition recomendation: eat tofu, tempeh, lentils (less amount of oxalate) as protein sources instead of legumes such as beans or chickpeas; avoid spinach, chocolate and nuts.
    Eat almonds, brocoli, zuchini, carrots, celery, peppers, onion, red cabbage, enough fruit and whole cereals.
    See how you are feeling with this changes. I hope this help you with the attacks.

    Yared, health support volunteer

  9. Science doesn’t support the idea that Oxalates are dangerous when eaten from whole foods naturally. Eat a balanced diet and don’t worry about these things. The research indicates there is something missing we don’t understand and that kidney stones are NOT caused by either plat calcium or plant oxalates.

  10. The clinical research on calcium is very mixed. At higher levels (1400mg/day) we see significant increases in premature death. I have not seen any studies that show a benefit though, even at lower levels of calcium intake/supplementation. If you encounter a well founded study, especially a meta-analysis that shows a benefit at a specific level, I’d like to see it. Of course the research funded by the dairy industry shows a benefit, but that doesn’t count.

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