When it comes to preventing kidney stones with diet, protein type and acid load may matter.

Pietro Manuel Ferraro, MD, of Catholic University of the Sacred Heart, in Rome Italy, and colleagues identified 6308 kidney stone cases during more than 3 million person-years of follow up in their analysis of 3 major cohorts. Consuming more non-dairy, animal protein was associated with 15% and 20% greater odds of kidney stones, respectively, in the all-male Health Professionals Follow-Up Study and the all-female Nurses’ Health Study I. A higher animal protein-to-potassium ratio, which approximates dietary acid load, also was associated with higher risks of kidney stones, independent of its constituents. Acid production from sulfur-containing amino acids is counterbalanced by alkali-containing potassium salts.

Vegetable protein intake did not appear to influence kidney stone risk, whereas dairy protein might have a mixed effect, according to the investigators.

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Greater potassium intake was associated with 33% to 56% lower risks of kidney stones in all 3 cohorts. According to urinary excretion results, higher dietary potassium intake was associated with higher urine citrate, pH, and volume—all conditions unfavorable to stone formation.

These results were not modified by age, body mass index, diabetes, hypertension, thiazide medications, or calcium supplements. The researchers also accounted for dietary intake of fluids, alcohol, calcium, sodium, fructose, oxalate, and phytate.

“Our data suggest that diets rich in fruits and vegetables as well as diets with a relative abundance of fruits and vegetables compared with animal protein may represent effective interventions to prevent kidney stone formation,” Dr Ferraro and colleagues concluded in the Clinical Journal of the American Society of Nephrology.

A 2009 study of the same cohorts likewise showed that an eating plan similar to dietary approaches to stop hypertension (DASH), which includes high amounts of produce and low intake of red and processed meats, related to decreased stone risk  (J Am Soc Nephrol 2009 Oct;20(10):2253-9).

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1. Ferraro PM, Mandel EI, Curhan GC, et al. Dietary Protein and Potassium, Diet–Dependent Net Acid Load, and Risk of Incident Kidney Stones. Clin J Am Soc Nephrol 11: 1834–1844, 2016. doi: 10.2215/CJN.01520216.