Fruits and Vegetables Fruits and vegetables contain organic acids bound to minerals – largely potassium, magnesium, and calcium – that are metabolized to bicarbonate in the liver. With higher circulating bicarbonate, the kidneys reabsorb less citrate, leading to higher urinary citrate. Citrate is a potent inhibitor of calcium phosphate and calcium oxalate kidney stone formation. When consumed in sufficient quantities, fruits and vegetables are therefore capable of increasing urinary citrate excretion and reducing calcium stone risk. Although hypocitraturia is not always attributable to dietary influences, patients with calcium stones and hypocitraturia should nonetheless be advised to consume ample fruits and vegetables. The quantity of fruits and vegetables needed to effectively raise urinary citrate varies among individuals and depends on baseline urinary citrate levels and other factors such as overall acid load of their diets, comorbidities, and genetics. Meschi et al. recommended six to seven daily servings of a variety of fresh fruits and vegetables in individuals with idiopathic calcium stones, hypocitraturia, and very low baseline fruit and vegetable consumption. They found that urinary citrate increased and other parameters had favorable changes compared to baseline with initiation of this intervention.151 However, in a meta-analysis comprising 13 studies evaluating the effect of dietary interventions to address hypocitraturia,152 only 3 studies (1 cross-over153 and 2 RCTs)27, 154 assessed the effects of a high-fiber diet from fruits, vegetables, and cereals on 24-hour urinary citrate excretion. Only the cross-over study showed an increase in urinary citrate with this intervention.153 Nonetheless, even without strong evidence from RCTs, ample fruit and vegetable consumption should be recommended to individuals who form any type of kidney stone and particularly to those with lower urinary citrate. Some established models for increasing intake of fruits and vegetables include Mediterranean-style diets, Dietary Approaches to Stop Hypertension (DASH) diet, Alternative Healthy Eating Index (AHEI), Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND), Planetary Health Diet Index (PHDI), and various vegetarian-style dietary patterns.155 Protein When dietary acid exceeds the capacity of the body to neutralize it with bicarbonate generated from alkali sources (i.e., fruits and vegetables), compensatory mechanisms include higher renal citrate reabsorption, resulting in lower urinary citrate excretion. See Statement 12 on foods associated with a high acid load and discussion of protein needs. Few high-quality studies have assessed the effects of dietary protein specifically on urinary citrate excretion among calcium stone-forming patients with hypocitraturia. Among healthy adults, Breslau et al. studied the effects of vegetable, egg, and animal protein and identified lower urinary citrate excretion on the diet higher for animal protein.156 A controlled metabolic cross-over study in healthy adults and a dietary intervention study among patients with calcium stone disease directly assessed effects of dietary protein on urinary citrate excretion. Knight et al. performed a 3-phase metabolic cross-over study in healthy adults comparing 3 different quantities of daily protein: low (0.6 g/kg of body weight/day), moderate (1.2 g/kg of body weight/day), and high (1.8 g/kg of body weight/day) in each phase.157 Urinary citrate excretion decreased with each phase of higher protein intake, although the difference did not consistently reach statistical significance. In a metabolic study of patients with idiopathic hypercalciuria and calcium stones (but not hypocitraturia), initiation of a lower protein diet (0.8 g/kg of body weight) resulted in a significant increase in urinary citrate in all patients.158 Despite a lack of high level evidence, the Panel supports the recommendation to avoid excessive total protein consumption and encourage higher plant protein consumption in patients with hypocitraturia.