Following a Dietary Approaches to Stop Hypertension (DASH)-style diet may help lower kidney stone risk by increasing urinary citrate and urinary volume, according to the results of a large cohort study reported online September 16 in the Clinical Journal of the American Society of Nephrology.

“We previously observed associations between a …DASH-style diet and large reductions in kidney stone risk,” write Eric N. Taylor, from Brigham and Women’s Hospital and Harvard Medical School in Boston, Massachusetts, and colleagues. “This study examined associations between a DASH-style diet and 24-hour excretions of urinary lithogenic factors.”

The study cohort consisted of 3426 adults with and without nephrolithiasis who were enrolled in the Health Professionals Follow-up Study (HPFS) and the Nurses’ Health Studies (NHS) I and II. A DASH score was calculated from self-reported dietary composition, with higher scores reflecting higher consumption of fruits, vegetables, nuts and legumes, dairy products, and whole grains, and lower consumption of sweetened beverages and red and processed meats. The investigators adjusted 24-hour urinary calcium excretion for age, history of kidney stones, body size, and other factors using analysis of covariance.

For participants in the highest vs the lowest quintiles of DASH score, multivariate-adjusted urinary calcium excretion was increased by 3% in HPFS (P for trend = .12), by 10% in NHS I (P for trend < .01), and by 12% in the NHS II (P for trend = .05). Compared with participants in the lowest quintiles of DASH score, those in the highest quintiles had 4% to 18% higher urinary oxalate (P for trend < .03 for all), 11% to 16% higher urinary citrate (P for trend < .01 for all), and 16% to 32% higher urinary volume (P for trend < .001 for all).

In addition, a higher DASH score was associated with greater urinary potassium, magnesium, phosphate, and pH, and lower relative supersaturations (RSS) of uric acid. Among women only, a higher DASH score was associated with lower RSS of calcium oxalate.

“A DASH-style diet may reduce stone risk by increasing urinary citrate and volume,” the study authors write. “The small associations between higher DASH score and lower RSS suggest unidentified stone inhibitors in dairy products and/or plants.”

Limitations of this study include use of 24-hour urine samples, which prevented identification of associations between a DASH-style diet and potentially important postprandial increases in lithogenic factors such as calcium and oxalate, and which is likely to reflect only short-term dietary intake. In addition, the participants in the study sample were all white, limiting generalizability.

“The higher oxalate content of a DASH-style diet does not lead to large increases in 24-hour urinary oxalate, a finding consistent with our previous reports of only small associations between oxalate intake and both urinary oxalate excretion and incident kidney stone risk,” the study authors conclude. “Overall, we believe our results provide a strong rationale for a randomized trial examining the effect of a DASH-style diet on kidney stone recurrence.”