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Low oxalate diet

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Also listed as: Diet, low oxalate
Related terms
Background
Theory/evidence
Safety
Author information
Bibliography
Diet outline

Related Terms
  • Calcium oxalate, calcium oxalate stones, diet, high oxalate, high oxalate diet, kidney stones, low oxalate, oxalate, oxalic acid, oxalis, short bowel syndrome, vulval pain, wood sorrel.

Background
  • A low oxalate diet eliminates foods and beverages of high oxalate concentration, often to treat kidney stones and other kidney disorders. Oxalate is a compound commonly found in foods of plant origin that strongly bind to minerals (e.g., calcium, magnesium, and potassium), and reduces their absorption. Foods that come from animals generally have little or no oxalate. This diet is frequently given to people who have increased levels of oxalic acid in their urine or who have a history of forming kidney stones (small pebbles that form in either the kidney or the bladder).
  • Oxalic acid's name comes from Oxalis spp. (wood sorrel) from which it was first isolated. This acid has the ability to form a strong bond with various minerals forming compounds referred to as oxalate salts. Therefore, oxalate generally refers to the salt form of oxalic acid, one of which is calcium oxalate.
  • About 1 in every 1,000 adults in the United States is hospitalized annually for kidney stones. Dietary factors may increase or reduce the risk of forming calcium oxalate stones. Nearly 80% of reported kidney stones in patients in the United States are composed of calcium oxalate.
  • Experts have known for a long time that oxalate is an irritant that may cause histamine release and burning in tissues. However, exposing healthy skin and nerves to oxalate does not result in pain. At high concentrations, oxalic acid may cause death in humans and animals due to its corrosive effects. In smaller amounts, oxalic acid may cause a variety of pathological disorders, including hyperoxaluria (an excessive amount of oxalate in the urine), vitamin B6 deficiency, cardiomyopathy (disease of the heart muscle that often leads to abnormal function), heart rhythm disorders, calcium oxalate stones and renal failure.
  • Currently, the low oxalate diet has strong evidence supporting its use in the treatment of kidney stones. However, this diet may not always be effective in reducing urinary oxalic acid levels because most oxalate found in urine is made in the body and not from dietary oxalate. Promising future uses for this diet may include treatment of short bowel syndrome, unexplained vulval pain and malabsorption of fat.

Theory / Evidence
  • There are two types of oxalates: calcium oxalate and oxalic acid. Oxalic acid is a strong organic acid, which is commonly found in both plants and animals. In the animal kingdom oxalate and its salts are present in the urine and blood of mammals. The oxalate in humans and animals comes from the oxalate ingested with plant material, although through the oxidation of glyoxalate and ascorbate they synthesize tiny amounts. Both sodium and potassium oxalate salts are water soluble; however, calcium oxalate is insoluble. Therefore, if calcium oxalate is present in high enough concentrations, it has a tendency to precipitate in the kidneys or in the urinary tract to form calcium oxalate crystals. It is not clear why women have a much lower frequency of kidney stones than men. Both men and women synthesize oxalate from a number of compounds that are precursors to oxalate.
  • Scientists once thought that the higher the oxalate concentration in food, the higher the risk of forming kidney stones. However, they have found that consuming certain foods and/or beverages containing oxalate are more likely to increase urinary oxalate. There remains no universal consensus on which oxalate-containing foods belong on high oxalate food lists. Nonetheless, there is growing awareness that people with a history of kidney stones should avoid certain high oxalate foods that are most responsible for increasing urinary concentrations of oxalate. The majority of the urinary oxalate obtained from food may appear in the urine 2 to 6 hours after the consumption of the food containing oxalate.
  • Oxalate is in many foods and binds to calcium in the body. Often they will they bind together in the stomach or intestines and then they will pass through the body and not get into the kidneys. But if oxalate does not find calcium to bind with in the stomach, it will get into the kidneys, find calcium to bind with there, and form stones.
  • Vitamin C metabolizes to oxalate and intake is often reduced during this diet. However, a Nurses' Health Study, Intake of vitamins B6 and C and the risk of kidney stones in women, analyzed over 85,000 women and found no increased risk of kidney stone formation with vitamin C intake.
  • People suffering from vulvodynia (lasting pain in the area around the opening of the vagina (vulva) or chronic vulvar pain) may often adhere to a low oxalate diet. Many patients typically combine this diet with treatments such as surgeries; antibiotics, antidepressants, antifungals, anti-inflammatory drugs; or most topical preparations. In one study, 31 women with vulval vestibulitis were evaluated for evidence of abnormal dietary oxalate intake and a wide range of dietary intakes was recorded. No woman was found to have abnormal urinary excretion. Sixteen women agreed to undertake a low oxalate diet and there was an apparent response in six (37%).
  • The American Society for Parenteral and Enteral Nutrition Clinical Guidelines states that a low oxalate diet may be appropriate for patients with short bowel syndrome (malabsorption resulting from anatomical or functional loss of a significant length of the small intestine) and an intact colon. Calcium oxalate kidney stones are a potential complication of short bowel syndrome. Dietary calcium in the stool normally binds to oxalate, not allowing it to be absorbed in the colon. Because of fat malabsorption, the calcium binds better to the free fatty acids in the stool. This leaves the oxalate free to be absorbed by the colon and may lead to hyperoxaluria and kidney stones. Nutritional management is thought to be the key factor in achieving an optimal outcome in short bowel syndrome. Patients with a short bowel and colon are often advised to follow a diet low in oxalate because 25% of the oxalate may develop as calcium oxalate kidney stones.

Safety




Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography
  1. Baggish MS, Sze EH, Johnson R. Urinary oxalate excretion and its role in vulvar pain syndrome. Am J Obstet Gynecol. 1997 Sep;177(3):507-11.
  2. Buchman AL, Scolapio J, Fryer J. AGA technical review on short bowel syndrome and intestinal transplatation. Gastroenterol 2003;124:1111-34.
  3. Curhan GC, Willett WC, Speizer FE, et al. Intake of vitamins B6 and C and the risk of kidney stones in women. Am J Obstet Gynecol. 1997 Sep;177(3):507-11.
  4. Jensen JE, Freese D. Kidney Stone Diet.
  5. National Kidney Foundation. Diet and Kidney Stones. .
  6. Nightingale JM. The medical management of intestinal failure: methods to reduce the severity. Proc Nutr Soc. 2003 Aug;62(3):703-10.
  7. Nishiura JL, Martini LA, Mendonca CO, et al. Effect of calcium intake on urinary oxalate excretion in calcium stone-forming patients. Braz J Med Biol Res. 2002 Jun;35(6):669-75.
  8. Poole S, Ravenhill G, Munday PE. A pilot study of the use of a low oxalate diet in the treatment of vulval vestibulitis. J Obstet Gynaecol. 1999 May;19(3):271-2.
  9. Sundaram A, Koutkia P, Apovian CM. Nutritional management of short bowel syndrome in adults. J Clin Gastroenterol. 2002 Mar;34(3):207-20.
  10. The Cleveland Clinic. Kidney Stones.
  11. Von Unruh GE, Voss S, Sauerbruch T, et al. Dependence of oxalate absorption on the daily calcium intake. J Am Soc Nephrol. 2004 Jun;15(6):1567-73.
  12. Vulvar Pain Foundation

Diet outline
  • To help prevent oxalate stones from forming, most low oxalate diets recommend limiting oxalates to 40 to 50mg per day.
  • Low oxalate foods have less than 2mg of oxalate per serving. A low oxalate diet encourages ample use of these foods. Moderate-oxalate foods have between 2mg and 6mg of oxalate per serving. On a low oxalate diet, the consumption of these foods is often limited to 3 to 5 times a week. High oxalate foods have more than 7mg of oxalate per serving. These foods are avoided on a low oxalate diet.
  • Other dietary modification associated with a low oxalate diet may include increased consumption of water and limiting vitamin C intake. The National Academies' Institute of Medicine recommends a total intake of dietary fiber to be 21 to 38 grams per day along with a low oxalate diet.
  • For those treating kidney stones, soft drinks, especially colas because they contain phosphoric acid, high intakes of sodium and grapefruit juice are typically avoided as it may enhance the risk of developing new kidney stones. Vitamin supplementation, especially calcium, may be necessary in some; a qualified healthcare professional and nutritionist should be contacted before making an decisions about diet and/or health conditions.

Copyright © 2011 Natural Standard (www.naturalstandard.com)


The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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