Low Oxalate Diet File:Raphaël - Les Trois Grâces - Google Art Project 2.jpg

WHY EAT A LOW OXALATE DIET?

Do you need a low oxalate diet?

Who does?

Who does not?

How can you tell?

I chose the gorgeous painting by Raphael that hangs in the Musée Condé Chantilly because three surpasses one.

Who Needs Low Oxalate Diet?

Most of all, those whose stones contain calcium oxalate crystals and urine oxalate enough to promote such stones.

Less so those with systemic diseases – bowel disease, malabsorption syndrome, bariatric surgery, and primary hyperoxaluria – that raise urine oxalate. Their diseases require many treatments, only one of them low oxalate diet.

Therefore, I write here for only patients without a systemic cause of stones.

Do Your Stones Contain Calcium Oxalate?

If your stones contain little or no calcium oxalate crystals, and urine oxalate itself poses no danger to your kidneys, low oxalate diet is silly.

On the other hand, if your stones do contain calcium oxalate crystals, how much? Traces of the crystal, less than 10 percent, hardly bring it to the foreground. Even 20 percent is marginal. Above 10 or 20 percent calcium oxalate crystals in stones, consider lowering urine oxalate if high enough to raise risk of stones.

If you do not know what crystals make up your stones, struggle to find old analyses. Send all new stones for analysis. Stone prevention means crystal prevention. Stones are made from crystalsHow can you prevent what you do not know?

But if all this fails, assume your stones contain calcium oxalate crystals because they are the most common kindEven thenkeep trying to get a stone analysed; you have built your treatment on a rickety foundation because a guess is just a guess. 

Does Urine Oxalate Raise Your Risk for Stones?

It Does in General

In Gary Curhan’s wonderful study, the three bars represent two female (red) and one male cohort observed for decades. Some became stone formers, most did not. Twenty four hour urine samples drawn from both groups permit calculation of the risk from urine oxalate.

When below 25 mg/day urine oxalate poses no increased stone risk vs. even less than 20 mg/d. Thereafter, risk rises with urine oxalate, and low oxalate diet can contribute to stone prevention if stones contain significant amounts of calcium oxalate crystals.

Although Curhan had no stone analyses, calcium oxalate – being most common – would have predominated by chance. This is why if you do not know what your stones are made of, and your doctor has no clue either – from seeing them, or from observations during surgery, you can make the same assumption Curhan made and guess calcium oxalate predominates.

It May In You

Avoid circularity. That urine oxalate levels exceed, for example, 30 mg/day, does not raise the probability that calcium oxalate crystals comprise a majority of your stones.

It is when calcium oxalate crystals make up a significant proportion of your stone crystals – over 20 percent as a first approximation, or when you have no idea what your stones are made of but employ the Curhan conjecture favoring calcium oxalate that urine oxalate excretion matters. When above 25 mg/d you have a reason to lower it.

Be careful here. Follow the logic. Keep that oxalate list in the drawer for now and think about what you just read. If the trail of ‘ifs’ lead you on to urine oxalate as a suspect and you are in the right group – no systemic diseases, no kidney risk from oxalate according to your physician – continue reading.

Raise Your Diet Calcium

Diet Calcium Lowers Urine Oxalate

To illustrate the effects of diet calcium I have gathered average urine oxalate and diet calcium figures from multiple research papers named by senior author.

Dot size shows mean diet oxalate – the largest 200 mg/day, smallest 50, and middle 100 mg/day.

In each study raising diet calcium lowered urine oxalate. Diet oxalate itself had little effect.

The small box at the upper right shows an extreme experiment. Eating 2,000 mg/d of diet oxalate and 1,200 mg of calcium, subjects excreted 80 mg/d of oxalate. Despite the massive diet oxalate, enough diet calcium – 4,000 mg/d lowered urine oxalate to 30 mg/d.

Be careful. No one wants to eat that much calcium. The experiment simply aimed to make a point. My point is you eat 1,000 to 1,200 mg of diet calcium, and be done with it.

In other words, for any reasonable range of diet oxalate, diet calcium strongly controls urine oxalate. For that reason, measure the urine oxalate during high calcium diet and decide if low calcium diet remains important.

Diet Calcium Protects Bone Mineral

Even without stones we should want abundant diet calcium. Based on thorough reviews of mineral balance USDA and its scientific advisors recommend 1,000 to 1,200 mg of diet calcium daily for all US people as a benefit to bone health.

Because idiopathic hypercalciuria affects a majority of calcium stone formers they benefit especially from high calcium diet. Some people with IH cannot maintain bone mineral balance even on the high calcium intakes recommended for normal people. Less than high calcium diet poses risk of bone disease in later life.

Diet Calcium Should Come From Food 

Like most people, stone formers without systemic diseases do well with just dairy products and need no supplements. Industry makes them sans lactose, sans fat, in all the forms diet restrictions require. One might say the 1,000 or 1,200 mg of diet calcium best comes by parts in all the meals. If so, diet oxalate will encounter diet calcium by chance most of the time, so calcium can reduce oxalate absorption and thence urine oxalate excretion.

What About Supplements?

Like with high calcium foods, calcium from supplements lowers absorption of oxalate when they meet during a meal. No meal, they serve no purpose. Worse, they can raise urine calcium and risk of stone.

Lower Your Diet Sodium

If high urine oxalate raises risk of stones, so does high urine calcium. Both count. But raising diet calcium can raise urine calcium. So if all you do is eat more calcium you may not stop forming stones. You need to do one other key thing.

The trick, the smart move, the center of the center: Keep diet sodium as low as possible.

Red dots are normal people, blue stone formers with idiopathic hypercalciuria. For both, urine calcium rises with urine sodium, and urine sodium – more or less – reflects diet sodium intake. Each dot represents an entire published study group. 

Modern diet recommendations for US people consider 100 mEq/d (2,300 mg) of sodium the tolerable upper limit. These diet guidelines do not concern stones but rather high blood pressure and bone disease, but even so fit well with our needs. You would want to lower your diet sodium below 2,300 mg/d even if you formed no stones, for your blood pressure and general bone health.

In fact, the ideal diet sodium is far below 2,300 mg, at 1,500 mg – or 65 mEq if you prefer.

With care for diet sodium, high calcium intake need not raise urine calcium and certainly will lower urine oxalate. Lower urine oxalate without any rise in urine calcium means a fall in stone risk and therefore fewer stones long term.

Low Oxalate Diet Seems Easier

What?

He tells me to obsess about my stone crystals, raise my diet calcium, and lower my diet sodium. Two diet changes!

Why not just lower diet oxalate in the first place and be done?

Low Oxalate Diet Serves Only One Purpose

Low oxalate diet provides no health benefits apart from stone prevention. The highest oxalate foods, some dark green leaves, have good nutritional value. No data support diet oxalate as cause of any significant diseases apart from kidney stones. If you need to rely only on low oxalate diet to lower your urine oxalate then the diet may need to be very strict and restrictive of otherwise good foods. Higher diet calcium makes it easier and allows for greater variety.

Low Oxalate Diet Has Never Been Tried as a Stone Prevention 

No one has yet published evidence that low oxalate diet itself prevents calcium oxalate stones. At most, trials of other agents or diets have specified some restrictions of diet oxalate.

High Calcium Low Sodium Diet Prevents Stones

US diet recommendations favor low sodium and higher calcium to prevent hypertension and bone disease. One formal trial proved this kind of diet prevents calcium oxalate stones.

That trial showed that a high calcium, low sodium diet reduced calcium oxalate stone recurrence in men with idiopathic hypercalciuria.

Over five years, stones were less (solid line) in men asked to eat 1200 mg of calcium, 200 mg oxalate, 65  mEq of sodium compared to men eating 400 mg/d of calcium, unrestricted sodium and oxalate (dashed line). The 200 mg of diet oxalate in the high calcium group was achieved simply by excluding very high oxalate foods like spinach and nuts.

Although diet calcium was twice as high, urine calcium in the low sodium group was the same as that of the low calcium controls (5.9 vs. 6.2 mmol/d). Even though diet oxalate was 200 mg/day, not very low, urine oxalate was lower in the high calcium group (333 vs. 411 umol/day – about 35 vs 43 mg/d) and it is this reduction that reduced supersaturation and presumably new stones.

So low oxalate diet has no trial but high calcium, low sodium diet has one trial, a positive one at that.

Low Oxalate Diet is Not Easy to Follow

I know that from the many comments on this site, from decades of practice, too. One can lower diet oxalate. Those who form calcium oxalate stones are well advised to be wary of high oxalate intake. But why strive to go below 200 mg of diet oxalate when you can just eat more calcium and less sodium which helps your bones and your blood pressure? Let us make that diet – higher calcium, lower sodium our goal. With it, you need not so much a ‘very low’ as a moderately low – 200 mg –  oxalate diet and that may be enough.

An Important Oxalate Authority Recommends a Lower Goal

Despite the one trial, Dr Ross Holmes favors somewhat less daily oxalate.

He wrote on this site: ‘Hi Dr. Coe. I think you have been too cavalier in setting 200 mg oxalate as an appropriate target oxalate intake. Several studies in individuals eating controlled diets with adequate amounts of calcium have shown that the average amount absorbed is 8% with about half of that occurring rapidly in the small intestine. That is about 8 mg of oxalate that will flood the kidney within an hour or two after ingestion. Those great studies of Dr. Curhan that you have often mentioned show that this amount of oxalate in urine will substantially increase the risk of forming stones.’ (italics added for clarity). 

Essentially Ross makes this point. The immediate inflow of oxalate from a 200 mg/day diet – if all 200 mg were eaten in one meal – could flood the urine with as much as 8 mg of oxalate in an hour or two (1/2 of 8% of 200 mg). That flooding could produce transient high urine oxalate concentrations. High diet calcium might not prevent such a happening. A lower goal of 100 mg offers what he might call an extra margin.

Ross is a wonderful scientist whose work has informed oxalate research for decades. So I tend to respond to what he says.

The transient flooding – stone risk mechanism presumably affected the Borghi trial. Flooding would matter less if one avoids eating all 200 mg of oxalate in one meal. But even so, I accept his comment and suggest that 100 to 200 mg is perhaps preferable to a simple 200 mg goal- with care to avoid eating all of it in one meal.

Let Us Focus Elsewhere and Better

High calcium, low sodium, and moderate oxalate seems the best plan. There is a trial of it. Three separate factors all point at stone reduction. Two of them, low sodium and high calcium confer health benefits beyond stone disease. As part of a threesome, diet oxalate lessens in intensity. The ‘list’ needs contain only the highest oxalate foods. The budget of 200 mg/day is large enough to permit considerable freedom.

More important than everything I have said so far. Do not begin with a reach for the oxalate list. The list at best adds value for some patients. You may not be that patient. You may not have an oxalate problem at all. If you do, higher diet calcium and lower sodium may solve your problem with a minimal effort toward diet oxalate.

Put your money on the high cards, on the best horses, the best teams.

In case you wonder about the three goddesses, it is for the three fold plan: Higher diet calcium, lower diet sodium, moderate diet oxalate. Not so pretty as they are, but good enough.

49 Responses to “WHY EAT A LOW OXALATE DIET?”

  1. Rob Lewis

    Hi Doc,

    Would a multi-vitamin with 250 mg. Calcium Carbonate/Dicalcium Phosphate be a problem? I’m now incorporating milk and kefir into my “post-stone” diet as well-

    Many thanks,
    Rob Lewis
    Raleigh, NC

    Reply
  2. Thomas

    Chives and radishes are high in oxalic acid, but they are also highest in calcium among vegetables. Isn’t that a paradox and do we still need to avoid them?

    Reply
    • jharris

      Hi Thomas,

      Sometimes the calcium is just not good enough to combat the extra oxalate. Like spinach. As far as chives, I would think the portion you use is not going to be big enough to make a difference in either category….but then maybe you are a chive-a-holic… my point is portion is key with most product.

      Best,
      Jill

      Reply
    • Fredric Coe, MD

      Hi Thomas, Not a paradox if you think about the plants. They use oxalic acid as an energy store as it is essentially a two carbon fatty acid. Packing it in their tissues as calcium oxalate crystals can be very efficient. So we often see oxalate and calcium together. I do not know the oxalate bio availability of these two foods, perhaps no one has measured it. I would suggests getting your calcium elsewhere and not using these overly much. Regards, Fred Coe

      Reply
  3. Le Ann Hoffman Grace

    I am looking for a recent update oxalate count list can you help me please

    Reply
  4. jim

    Dear Dr. Coe:

    I have diagnosed with hyperoxaluria and as to cause was told “No, the cause is unknown. You just have it. ”

    *Is there a class of hyperoxaluria with no known cause?*

    Age 61, stone history.
    Diet restrictions did little; nor additional calcium; no symptoms of other disorders and now seen 2-3 metabolic experts, as well as regular urologist. No sign of genetic Primary Hyperaxaluria.

    Since 2014, 24-hour urine UrOx:
    162 | 160 | 668 * | 56 | 65 | 86 | 133** | 51 | 112 | 46
    *668 is probable error
    **133 is only one done with Litholink
    All other urine/serum values normal, including Calcium and Citrate; uric acid controlled by Allopurinol.

    Thanks for any thoughts.

    Reply
    • Fredric Coe, MD

      Hi Jim, Given that your urine oxalate can be as low as 56 and 46, I wonder about diet calcium. Likewise about your diet. If you use extra food calcium to achieve 1200 mg daily, and be sure the high calcium foods come with the main meals, perhaps the urine oxalate will stay at the lower end of your range. Primary hyperoxaluria does not go as high as 160 AND fall to 46. I suspect food calcium was not synchronized to the main meals. If you do increase calcium as noted, urine calcium may well rise a lot, whereupon low sodium will reduce it again. As for HOX, no it never has no cause. You do not ever just have it. Try what I suggest and let me know. Regards, Fred Coe

      Reply
      • jim

        Thank you.
        Due for another 24 hour urine soon; will check back.
        note:
        –Calcium supplement began with 4th test (56) and is taken with meal ONLY when no dairy (usually plain yogurt) with meal. Calcium Citrate (20% element calcium) .
        –Low sodium diet for many years (not perfect)

        The 56 urine Ox was with calcium AND “low Oxalate diet” (impossible diet!)
        Urine calcium never high; once low.

        –Will check back. Thanks for your writings, very helpful.

        Reply
        • Fredric Coe, MD

          Hi Jim, I am not sure I understand, but guess the urine oxalate was 56 even when you used high calcium diet of 1000 to 1200 mg daily eaten with main meals that had your oxalate in them; also a low oxalate diet. That does seem a bit unfortunate, and perhaps you have some reason for such a high persistent oxalate. I gather you are now adding calcium, but try to stay within 1200 mg daily as a total. Regards, Fred Coe

          Reply
          • jim

            “high persistent oxalate” – yes, this is my understanding. Even with Calcium supplement and lot of yogurt. 56 was on low-oxalate diet (ie counting mg oxalate)
            For completeness, here are urinary and serum calcium numbers for the 24-hour labs (since 2014)
            Several doctors (in Portland, Ore) have reviewed, but can identify no cause:

            162 | 160 | 668 * | 56 | 65 | 86 | 133** | 51 | 112 | 46 (urine oxalate)
            169 | NA | 150 | 146 | 175 | 58 | 78 | 188 | 257 | NA (urine calcium, 24)
            9.5 | NA | NA | 9.6 | 9.5 | 9.9 | 9.3 | 9.8 | 9.7 | NA (serum calcium)

            Reply
            • Fredric Coe, MD

              Hi Jim, What catches my eye is the variability in urine calcium. I propose this as something you and your physicians can consider. Perhaps try a true 1200 mg calcium diet using real foods, seeing to the calcium with meals that might contain oxalate. Keep a diet diary for the days before and during the collection. Be attentive to urine creatinine so collections match. Since the lowest oxalate values 46, 51 are mundane, I deeply suspect diet calcium as too low or the calcium not matching the oxalate intake times. But I may be wrong, thus the suggestion. If you were nearer by we have had an open CRC project for years that could have settled this, but it is closing and you are distant. Let me know, and best regards, Fred Coe

              Reply
              • jim

                I’ve been as Bangkok for treatment! Can you send me link to CRC project? I will review with my doctors. Know Hyde Park well (grad school) and eager to ‘settle’ this if possible. Have all diet records.
                Thanks.

              • Fredric Coe, MD

                Hi Jim, I have forwarded your email to Elaine Worcester who is running the research protocol. She will no doubt be getting back to you. eworcest@bsd.uchicago.edu Best, Fred

  5. Anna

    Dear Dr. Coe,
    Thank you so much for your informative site. I am 63 y/o female who just passed my first ever stone – the analysis showed it was 85% oxalate. My urologist now informed me that I should go on a low oxalate (<50mg/day) diet. I'm a scientist myself, and after reading your site and the literature, I think your advice to increase dietary calcium and lower sodium, with moderate oxalate, is the way to go. How do I explain this decision to my urologist? Is there a position paper or review that I can give to him as evidence?
    Thanks again. Your column is a beacon in a sea of confusion about dietary oxalate.
    Anna

    Reply
    • Fredric Coe, MD

      Hi Anna, The web article is linked out to the source papers that are on PubMed. For example, the data on effect of diet calcium on urine oxalate come from the main article on treatment of idiopathic calcium stone formers. The graph is shown there and the text has a link to the original data sets. Here is the link. The references are linked on the sheet. The combination of low sodium, high calcium and moderated oxalate is the Borghi trial that is in the article you are commenting on. It links back to the treatment article that has a link to the original trial paper. But even without that, the figure is from the trial paper and has the reference in it. So, the web article is referenced enough and the URL would be fine. Put another way, although this is a website it is referenced like a textbook or review. Regards, Fred Coe

      Reply
  6. Donald Derrah

    I have Kidney stones, I had them treated by lithotripsy 7 years ago. But they are back, i have one that is 10mm. I looked through my medical file and I can not find any urine test for oxalates. Can you tell me what the name of the test should be. And would it probably be the same here in Canada.

    thank you

    Reply
    • Fredric Coe, MD

      Hi Donald, The test name would be urine oxalate. I am not sure the measurements are at all the same in Canada as I have seen some results that are too low to believe. But that is what to look for. Regards, Fred Coe

      Reply
      • Donald Derrah

        Thank you. I am starting the test tomorrow. Appreciate the info

        Reply
  7. Genna

    Hi. This is interesting news and a relief for my adolescent daughter who doesnt have kidney stones but suffer pain in urination and burning skin, particularly after nuts, dates or a smoothies(spinach). I will try calcium, low sodium and be more mindful of levels without depressing her further with a new ‘diet’ where she feels overwhelmed what she cannot have. thank you

    Reply
    • Nancy Benefield

      Hi Genna,
      IS your daughter having an allergic reaction to these foods? If so is she using any type of inhalers or other allergy medications. These sometimes can cause pain on urination as a side effect.

      Reply
  8. Sheldon Haversham

    Hi Dr. Coe, thank you for addressing my comment on the Crystal Light page. I enjoyed reading this one as well.

    Here is an article http://www.bestchinanews.com/Health/7301.html , regarding drinking Tea with Milk as a means of reducing its Oxalic acid absorbability (although another article mentions that Black Tea is not very absorbable in the first place). I wonder if the English across the pond who incessantly drink Tea with milk in, have increased their calcium intake significantly enough to reduce kidney stones on a national level in comparison to the US. The article also states, “Intestinal probiotics can degrade oxalic acid”.

    I also liked to share with everyone this article https://www.researchgate.net/publication/308962080_Addition_of_calcium_compounds_to_reduce_soluble_oxalate_in_a_high_oxalate_food_system

    Another article mentions that high oxalate foods differentiate in their absorbability which I think could hint to a more honed approach to eating oxalic acid rich foods. This is the list of foods that the University of British Columbia stated had oxalates that were absorbable “peanuts, pecans, wheat bran, spinach, rhubarb, beets and beet greens and chocolate. While other foods are considered high in oxalic acid, studies have not shown that the body readily absorbs their oxalate content. These include soy foods, sweet potatoes, black tea, berries and other dark leafy greens, like Swiss chard and collards.” http://healthyeating.sfgate.com/oxalic-acid-foods-8447.html

    Yet another interesting article calls for the modification of our crop growing methods by which it proved it could reduce the oxalic acid in spinach by 2/3rds, which would increase the calcium bioavailability from spinach. http://www.techbriefs.com/component/content/article/ntb/tech-briefs/bio-medical/498

    Lastly, here is an article that states that a study on the low oxalate diet shows it reduces the risk of kidney stones by 14% while the DASH diet reduces it by 35%.

    Thanks again Dr. Coe.

    Reply
    • Fredric Coe, MD

      Hi Sheldon, The effects of calcium intake on urine oxalate are much more accurately documented on the site, as I actually compiled the data from the only available experiments into a usable graph. The graph is in the article to which you have appended this very note!

      The material about low oxalate diets and stones are not as you say. They are not trials but epidemiological associations between remembered diet intake and new onset of stones. No trials exist for low oxalate diet.

      As for bioavailability of food oxalate, my only authority is Dr Ross Holmes who did much of what we have available, and he does not agree that these foods are indeed more safe.

      Best, Fred Coe

      Reply
      • Sheldon Haversham

        Thank you Dr. Coe for your insight and help. Could you help me find the list of foods which Dr. Holmes deems less bioavailable in regards to oxalates and maybe also the ones that really bad for you. Thank you, Sheldon

        Reply
        • Fredric Coe, MD

          Hi SHeldon, The food lists in this article are graded from bad to better. I would advise avoiding those in the top 20 – look at the graph in the article that shows the worse 89 foods. Perhaps the top 30. Then, recheck your urine and see if your oxalate is still above the stone risk of 25 mg/day. If so, go down 10 more on the graph. Regards, Fred Coe

          Reply
          • Sheldon Haversham

            Thank you for the link and the advice. I’ve read of the high oxalate content of date fruits and its listed as 24 in just one date. I wonder if it was a specific variety being tested. As I understand it, there are a multitude of varieties. The two I’ve been exposed to on the market are Mejdool dates & Deglet Noor dates. They are easy to eat, high in fiber & potassium and have other benefits. I wondered which type were tested. I found a pdf, which I’ll provide, that tested 8 different varieties which I’ve never heard of but one, Deglet Noor, which they recorded as “Total oxalate (g/100 ml) 0.432±0.038”. In the opening paragraph of the paper it stated that the 8 date varieties they tested were low in oxalates. I don’t understand the values they attributed to the Deglet Noor variety. Are they in fact low in oxalates? If the values are low, can the source of the study, in your opinion, be trusted? https://www.ajol.info/index.php/ajb/article/download/80650/70891

            Reply

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