A diet rich in fruits and vegetables, moderate in low-fat dairy products, and low in animal protein may reduce the risk of kidney stones by increasing urinary citrate and volume, according to researchers.

Eric N. Taylor, MD, of Maine Medical Center in Portland and Brigham and Women’s Hospital/Channing Laboratory in Boston and colleagues examined associations between a Dietary Approaches to Stop Hypertension (DASH)-style diet and 24-hour excretions of urinary lithogenic factors. The study included 3,426 participants with and without nephrolithiasis in the Health Professionals Follow-up Study (HPFS) and the Nurses’ Health Study (NHS) I and II. The HPFS included 51,529 male health professionals between the ages of 40 and 75 at enrollment in 1986. NHS 1 included 121,700 female registered nurses between the age of 30 and 55 years at enrollment in 1976. NHS II included 116,430 female registered nurses between the ages of 25 and 42 at enrollment in 1989.

Dr. Taylor’s group calculated a DASH score based on seven components: high intake of fruits, vegetables, nuts and legumes, dairy products, and whole grains, and low intake of sweetened beverages and red and process meats.

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Comparing the highest versus lowest quintiles of DASH score and after adjusting for age, kidney stone history, body size, fluid intake and other factors, subjects in HPFS, NHS I, and NHS II had 18%, 7%, and 4% greater oxalate excretion, respectively, and 11%, 12%, and 16% greater citrate excretion, respectively, according to an online report in the Clinical Journal of the American Society of Nephrology. In addition, they had 16%, 28%, and 32% greater urinary volume, respectively. All of these differences between the highest and lowest quintiles were statistically significant.

The authors explained that although the higher oxalate content of a DASH-style diet—the result of higher intakes of fruits, vegetables, and nuts—would be expected to increase urinary oxalate, the higher calcium intake associated with the diet may minimize this effect. Greater consumption of fruits and vegetables also increases urinary citrate, an important inhibitor of calcium stones, the researchers pointed out.

In a previous prospective analysis of data from the larger study populations, a team led by Dr. Taylor showed that, compared with HPFS subjects in the lowest quintile of DASH score, those in the highest quintile had a 45% reduced risk of kidney stones after adjusting for age, BMI, fluid intake, hypertension, diabetes and other potential confounders, Dr. Taylor’s team reported in the Journal of the American Society of Nephrology (2009;20:2253-2259). Among subjects in NHS I and NHS II, those in the highest quintile had a 42% and 40% reduced risk of kidney stones compared with the lowest quintile.