DASH-Style Diet May Help Protect Against Kidney Stones

From Medscape Medical News
Laurie Barclay, MD

August 18, 2009 — The Dietary Approaches to Stop Hypertension (DASH) diet may help protect against kidney stones, according to the results of a prospective study reported online August 13 in the Journal of the American Society of Nephrology.

"Despite previously observed associations between individual dietary factors and kidney stone risk, relatively few studies have examined the impact of overall diet or dietary patterns on risk," write Eric N. Taylor, MD, from Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, and colleagues.

"The [DASH] diet, which is high in fruits and vegetables, moderate in low-fat dairy products, and low in animal protein represents a novel potential means of kidney stone prevention. The consumption of fruits and vegetables increases urinary citrate, an important inhibitor of calcium stone formation, and a diet with normal to high calcium content but low in animal protein and sodium decreases the risk of calcium oxalate stone recurrence by 51%," the researchers state.

The investigators studied the association between a DASH-style diet and incident kidney stones in the Health Professionals Follow-up Study (n = 45,821 men; 18 years of follow-up), Nurses' Health Study I (n = 94,108 older women; 18 years of follow-up), and Nurses' Health Study II (n = 101,837 younger women; 14 years of follow-up).

To determine degree of compliance with the DASH-style diet, the investigators constructed a DASH score based on 8 components: high consumption of fruits, vegetables, nuts and legumes, low-fat dairy products, and whole grains, and low consumption of sodium, sweetened beverages, and red and processed meats. Cox hazards regression allowed adjustment for age, body mass index (BMI), fluid intake, and other clinical factors.

During a combined follow-up of 50 years, there were 5645 incident kidney stones. Intakes of calcium, potassium, magnesium, oxalate, and vitamin C were higher in participants with higher DASH scores, and sodium intakes were lower.

The observed reductions in kidney stone risk were independent of age, BMI, fluid intake, and other factors. Even in participants with lower calcium intake, higher DASH scores predicted lower risk for kidney stones. The findings were unaffected by excluding participants with hypertension.

"Consumption of a DASH-style diet is associated with a marked decrease in kidney stone risk," the study authors write. "In contrast to our previous studies of individual dietary factors and kidney stone risk in these populations, the impact of a DASH-style diet was similar in men and women, in older and younger individuals, and in participants with both low and high BMI."

Limitations of this study include lack of data on stone composition reports from all stone formers, failure to examine the effect of DASH score on 24-hour urine calcium, poor measurement of sodium intake, and limited generalizability.

"Although we think it reasonable for calcium oxalate stone formers with high levels of urinary oxalate to avoid intake of some individual foods very high in oxalate (such as spinach and almonds), our data do not support the common practice of dietary oxalate restriction in calcium stone formers, particularly if such advice results in lower intake of fruits, vegetables, and whole grains. Because of the adverse side effect profile of many current medical therapies for nephrolithiasis, a randomized trial is needed to determine the efficacy of a DASH-style diet compared with medical intervention for the secondary prevention of calcium oxalate kidney stones."


J Am Soc Nephrol. Published online August 13, 2009.