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Oxalate

For Patients

If you suspect you have stones, visit your primary care provider or urologist.

If you've been diagnosed with stones and would like to be seen in the Metabolic Stone Clinic, please call (608) 263-4757.

Nutritional recommendations for addressing oxalate as a means of reducing the risk of kidney stones are some of the most complex and misunderstood. Approximately 20 percent of individuals who form calcium oxalate stones have hyperoxaluria (high oxalate in their urine). These individuals benefit from a reduction in high-oxalate foods. However, the vast majority of those with calcium oxalate stones, whose urine oxalate is normal, do not benefit from a restriction of high-oxalate foods. As foods containing oxalate also happen to be quite beneficial for overall health, providing essential nutrients, fiber, antioxidants and other important phytochemicals, an oxalate restriction should be considered individually, based on the individual stone former's unique risk factors.
 
The foods known to cause a high urinary excretion of oxalate are:
 
  • Spinach, rhubarb, beets (both the root and the greens), nuts and nut butters, chocolate and cocoa, green and black tea, wheat bran (in high amounts), soybeans and foods made from soy, and strawberries.
  • Other foods commonly held to contain high oxalate, such as cola beverages and coffee, do not actually contain much oxalate. Stone formers may consume these beverages in moderation as part of an overall healthy diet.
If you absorb too much oxalate from the foods in your diet, your risk for calcium oxalate stones increases dramatically. How does oxalate absorption get too high?
 
  • Some individuals lack the enzyme necessary to break down oxalate in the gastrointestinal tract. These individuals have primary hyperoxaluria type 1 (more severe) or 2 (less severe). Even a severe oxalate restriction will not cure these individuals from their disease, but it may reduce their risk for stones.
  • Some individuals have enteric hyperoxalauria, meaning that their intake of the plant foods that are rich in oxalate is too high for their GI tract to handle. These individuals benefit from a restriction of high-oxalate foods. (Interestingly, though, studies show that vegetarians, whose oxalate intake is typically two to three times that of non-vegetarians, actually have a lower risk for calcium oxalate kidney stones.)
  • Other individuals absorb too much oxalate because: (a) their dietary fat intake is too high; (b) their calcium intake is too low; or (c) their calcium intake is adequate but not timed with meals. Oxalate is fat-soluble, so reducing the fat you eat, especially saturated fat, may reduce the amount of oxalate you absorb. What about the calcium-oxalate connection? Oxalate absorption is dramatically decreased with an appropriate amount of calcium (approximately 1000 mg/day for most individuals), consumed in divided doses at meal times, when you are most likely to consume plant foods that contain oxalate. Thus, individuals who don't require a severe oxalate restriction can still eat those healthy foods if they take care to have a small glass of milk or other calcium-rich food at every meal. When the oxalate and the calcium are present in the GI tract at the same time, they bind together and neither is absorbed.
 
To determine if you need an oxalate restriction, your 24-hour oxalate excretion should be known and your calcium intake should be assessed. A Registered Dietitian can help you determine whether you need an oxalate restriction, a change in your calcium intake, or both.
 
Other strategies that may be suggested to reduce urinary oxalate excretion include vitamin B6 (also known as pyridoxine) in high doses and probiotic therapy. Vitamin B6, which is available over the counter in 25- or 50-mg tablets, may reduce the amount of oxalate your body produces. Subsequent analysis of your 24-hour urine will determine if this therapy is successful. Probiotic therapy with bacteria of the oxalobacter and possibly lactic acid type may be useful to reduce urinary oxalate; studies are pending. Talk with your physician about it.