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.
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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.