Numerous studies have shown the effects of different types of nutritional intervention on urinary risk factors for the formation of kidney stones, but the evidence from randomized trials is still low and of uncertain meaning. The effectiveness of protein restriction has been evaluated in several studies that still do not allow definitive conclusions to be made owing to the heterogeneity of experimental designs. In this study, protein restriction in combination with salt restriction and a calcium intake normalized according to the levels of intake recommended for the general population was more effective than a low-calcium diet. However, the effect of the reduction in protein intake cannot be distinguished from that of salt restriction and, in turn, the overall effect of this diet cannot be well estimated because the control group was on a diet potentially favoring the formation of stones. This Recommendation is of an article referenced in an F1000 Faculty Review also written by Giovanni Gambaro and Alberto Trinchieri.