Eating foods with high oxalic acid content may contribute to high urine oxalic acid levels and formation of oxalic acid-based kidney stones -- the most common type of kidney stones. Research does not indicate that high dietary oxalic acid intake is the most dominant factor in kidney stone development, however. Other factors and the absence of specific intestinal bacteria may be equally or more important contributors to high urine oxalic acid levels and risk of kidney stone development.
Oxalic Acid in Common Foods
Oxalic acid, or oxalate, is a substance found in many plant foods. Certain green leafy vegetables, such as beet greens, rhubarb and spinach, are among the foods with the highest oxalic acid content, with anywhere from 380 to 1440 milligrams in a 3.5-ounce serving. Almonds, cashews, peanuts, wheat and rice brans, okra and chocolate may contain from 50 to 250 milligrams per serving. In a study of about 240,000 people published in the July 2007 issue of “Journal of the American Society of Nephrology,” spinach was found to be the highest dietary contributor to an average daily oxalic acid intake of about 200 milligrams.
Your body’s tissues cannot break down oxalic acid. Your kidneys must filter it from the bloodstream and excrete it with the urine. Low urine volume, high urine oxalic acid levels or a combination of both factors can result in an amount of oxalic acid in the urine that exceeds the ability of the kidneys to keep it in solution. An overload of oxalic acid in the urine results in a condition called supersaturation. In supersaturated urine, the excess oxalic acid combines with calcium and forms insoluble salt crystals called calcium oxalate. These can accumulate in kidney tissue and develop into kidney stones. Increasing your fluid intake, which increases your urine volume, can help prevent stone formation.
Oxalic Acid Levels
Many factors other than dietary oxalic acid intake influence urine oxalic acid levels. For example, calcium can form a complex with oxalic acid in the intestines and prevent its absorption. The absence of bacteria that break down oxalic acid in the large intestine results in higher oxalic acid absorption. Your body also makes oxalic acid from a compound called glyoxal. The latter is found in foods, and it can be produced naturally in your tissues from vitamin C, carbohydrates and fats. According to the September 2008 issue of “Clinical Journal of the American Society of Nephrology,” being overweight or having diabetes may increase urine oxalic acid levels.
Avoiding foods with high oxalic acid content can certainly help reduce urine oxalic acid levels and lower your risk of getting kidney stones. Lowering your intake of foods rich in glyoxal, such as fermented foods and foods that have been roasted, baked or fried, may help reduce the amount of oxalic acid that your tissues produce. Following an eating plan such as the DASH diet -- Dietary Approaches to Stop Hypertension -- may be a reasonable alternative to a low-oxalic acid diet for people with oxalic acid kidney stone disease, according to a clinical study published in the March 2014 issue of “American Journal of Kidney Diseases."