What are the hazards of oxalates?

What are the hazards of oxalates?

Image Credit: Keith Hall/ flickr

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

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