Kidney stones are not all the same; they're made of different material and occur for different reasons in different parts of the urinary tract. The most common type of kidney stones consist of calcium oxalate or calcium phosphorus, according to the National Institute of Diabetes and Digestive and Kidney Diseases. Foods high in oxalate, such as cashew nuts, can increase your urinary excretion of oxalate and increasing your risk of developing calcium oxalate stones.
Stone Formation
Not everyone who has a high oxalate intake develops kidney stones. The risk of developing kidney stones increases with age in men and peak in the 50s for women. A history of urinary tract infections, hereditary metabolic diseases such as renal tubular necrosis and chronic bowel inflammation, which affect nutrient absorption, can increase the risk of stones. While dietary oxalate may reduce the risk if you're prone to kidney stones, a high intake doesn't necessarily cause stones, the NIDDK explains.
Intake
Taking in no more than 50 milligrams of oxalate per day helps reduce the chance of calcium oxalate stone formation if you're prone to stones, gastroenterologst Dr. Frank Jackson of Pennsylvania-based Jackson/ Siegelbuam Gastroenterology states. Nuts are one of the eight foods highest in calcium oxalate, along with beets, chocolate, rhubarb, spinach, strawberries, tea and wheat bran. A 1/4-cup serving of cashew nuts contains a high amount of oxalate, between 26 and 99 milligrams. Other nuts high in calcium oxalate include hazelnuts and pecans, while macadamia nuts, walnuts and pistachio nuts fall into the moderate oxalate category, with 10 to 25 milligrams per 1/4-cup serving.
Prevention
Outside of avoiding high-oxalate foods such as cashews or limiting their intake, drinking plenty of fluids is one of the best ways to prevent calcium oxalate kidney stone formation. The goal of increased fluid intake is to produce at least 2 quarts of urine per day, to wash out the excess oxalate, Jackson explains. To accomplish this, drink 8 to 10 ounces of water each hour during the day and one glass during the night, with at least 50 percent of fluids in the form of water.
Considerations
Kidney stones tend to recur, so if you've had one, you're likely to have another unless you take dietary measures to decrease your risk. Medications that control the acidity of the urine may also help since calcium oxalate stones tend to form in acid urine. High dietary calcium intake does not cause kidney stones, according to the NIDDK, although an inherited condition that causes higher-than-normal amounts of calcium absorption may cause stones. Avoid calcium supplements, which, unlike foods high in calcium, can increase your risk of forming calcium oxalate stones.
References
- Jackson/Siegelbaum Gastroenterology; Kidney Stone Diet; Frank Jackson, M.D.
- The Oxalosis and Hyperoxaluria Foundation: The Oxalate Content of Food
- National Institute of Diabetes and Digestive and Kidney Diseases; Kidney Stones in Adults; October 2007
- Urostone Center: Kidney Stone Anatomy
- National Institute of Diabetes and Digestive and Kidney Stone Diseases; Diet for Kidney Stone Prevention; May 2009
