Plant and Animal Protein Intakes and Risk of Incident Kidney Stones: Results from the Shanghai Men's and Women's Health Studies.

Purpose: High animal protein intake is a risk factor for nephrolithiasis. Whether plant based sources of protein are associated with kidney stone risk is not well studied. We examined the association of animal and plant protein intake with the risk of incident kidney stones in Shanghai, China. Materials and Methods: Dietary intakes were obtained from a validated food frequency questionnaire at baseline. Self-reported stone events were ascertained at baseline and at followup visits. Multivariable Cox regression models were used to evaluate the associations of protein intake with the incident stone risk. Results: During 319,211 and 696,950 person-years of followup 1,451 men and 1,202 women, respectively, reported incident stones. The average +/- SD intake of animal and plant protein standardized to 2,000 kcal was 31.3 +/- 13.7 and 48.4 +/- 7.2 gm per day in women, and 30.8 +/- 13.3 and 51.3 +/- 7.6 gm per day, respectively, in men. On multivariable analysis participants in the highest quintiles of animal and nondairy animal protein intake showed an increased risk of incident stones compared to those in the lowest quintiles (HR 1.16, 95% CI 1.01-1.32, p=0.03 vs HR 1.14, 95% CI 1.01-1.30, p=0.04). Compared to the lowest quintile the highest intake quintiles of the animal-to-plant protein ratios and the nondairy animal-to-plant protein ratios were positively associated with stone risk (HR 1.17, 95% CI 1.03-1.33, p=0.02 and HR 1.20, 95% CI 1.06-1.36, p=0.005, respectively). No association was observed with plant protein intake (p(trend)=0.14). Conclusions: In this population with a relatively low animal protein intake and a high plant protein intake, a greater animal protein intake was associated with a kidney stone risk. Increasing the proportion of plant protein relative to animal protein appeared protective against the risk.