The effect of fruits and vegetables on urinary stone risk factors

Background. The overall effect of fruit and vegetable intake on urinary stone risk profile is not yet known. Methods. We studied the effect of a two-week period of fruit and vegetable elimination on urinary stone risk profile in 12 normal adults, and of supplementing the diet with a fair quantity of low-oxalate fruits and vegetables in 26 idiopathic calcium stone formers characterized by hypocitraturia and a very low fruit and vegetable intake in their usual diet. Results. In the normal subjects, the elimination of fruits and vegetables from the diet decreased the urinary excretion of potassium (−62%), magnesium (−26%), citrate (−44%) and oxalate (−31%), and increased that of calcium (+49%) and ammonium (+12%) (P < 0.05 for all). The relative saturation for calcium oxalate and calcium phosphate increased from 6.33 to 8.24 (P = 0.028), and from 0.68 to 1.58 (P = 0.050), respectively. In the hypocitraturic stone formers, the introduction of these foods in the diet increased urinary volume (+64%), pH (from 5.84 to 6.19), excretion of potassium (+68%), magnesium (+23%), and citrate (+68%), while it decreased the excretion of ammonium (−18%) (P<0.05 for all). The relative saturation for calcium oxalate and uric acid fell from 10.17 to 4.96 (P < 0.001), and from 2.78 to 1.12 (P = 0.003), respectively. Conclusion. The total elimination of fruits and vegetables in normal subjects brings about adverse changes in the urinary stone risk profile that are only partially counterbalanced by a reduction in oxalate. In contrast, the addition of these foods to the diet of hypocitraturic stone formers not used to eating them not only significantly increases citrate excretion without affecting oxalate excretion, but also decreases calcium oxalate and uric acid relative saturation.