Dietary recommendations in patients with calcium phosphate and/or calcium oxalate stones in the setting of idiopathic hypercalciuria should focus on reducing urinary calcium excretion while supporting nutrient intake adequate to support optimal health and function. When hypercalciuria is truly idiopathic, dietary contributors are likely not responsible. However, specific dietary factors that influence urinary calcium excretion should be addressed. Calcium Excessive calcium intake can increase urinary calcium excretion. Although low calcium intake in patients with hypercalciuria may reduce urinary calcium, many patients will continue to excrete more calcium than they ingest due to calcium wasting from bone. Therefore, a first-line goal is to ensure calcium consumption that is neither too little nor too much, providing sufficient calcium for bone health but not excessive calcium that will increase stone risk. Calcium needs vary by age, gender, and life stage (Table 6). Calcium homeostasis is tightly regulated via a complex interplay of hormonal, genetic, physiologic, and dietary factors. Several large observational cohort studies in men and women in the United States demonstrated a higher risk of incident kidney stones with lower versus higher calcium intake,132-135 underscoring the concept that strict dietary calcium restriction should be discouraged. Data from interventional studies further support the importance of adequate calcium intake. In an RCT involving Italian men with hypercalciuria and a history of calcium oxalate stones, a normal-to-high dietary calcium intake (approximately 1,200 mg/day) was associated with a significantly lower stone recurrence rate compared to a low calcium diet (approximately 400 mg/day).29 However, the higher calcium diet also included lower salt intake and a higher proportion of plant-based protein relative to protein from animal sources, which may have contributed to the observed differences between groups. Calcium from foods and beverages, which provide other beneficial nutrients, are preferred over calcium supplements. Non-dairy, calcium-rich foods and beverages, often products fortified with calcium, are good alternatives for those limiting or avoiding dairy consumption. Ideally, calcium consumption should be distributed throughout the day; timing with meals is a good strategy for making this a routine habit and for binding to intestinal oxalate. Salt (sodium chloride) Sodium intake is one of the major dietary determinants of urinary calcium excretion.136-138 Higher dietary sodium directly impairs renal calcium reabsorption, resulting in greater urinary calcium excretion. Sodium chloride-induced metabolic acidosis also contributes to calcium resorption from bone and higher urine calcium.139 Because the adult human need for sodium is far below typical sodium consumption, the kidney excretes nearly all ingested sodium (95-99%) under steady-state conditions, with only minor losses through sweat and stool.140 The primary sources of sodium chloride in the American diet are breads and baked goods, cold cuts and cured meats, pizzas, soups, sandwiches, cheeses and foods made with cheese, and savory snacks. Interestingly, added salt (i.e., added to foods during cooking or at the meal) accounts for only around 10% of daily sodium intake in most individuals.141 In an RCT involving 197 patients (including both men and women) with hypercalciuria and calcium stone disease, Nouvenne et al. observed a 64 mg decrease in urinary calcium with a 100 mmol reduction in urinary sodium.142 Borghi et al. incorporated low salt dietary recommendations with normal-to-high calcium intake and lower consumption of animal protein and demonstrated lower stone recurrence rates over 5 years compared to a low calcium diet alone in an RCT involving hypercalciuric men.29 Of note, urinary calcium was not higher in the normal-to-high calcium group compared to the low calcium group. Individuals with hypercalciuria and higher salt consumption should be advised to limit salt intake. Common sense strategies for limiting salt include replacing salty foods and beverages with unsalted or low sodium counterparts (e.g., unsalted versus salted nuts, low-salt versus regular vegetable juices, non-marinated meats versus those marinated in salty marinades), eating smaller portions of salty foods, eating salty foods less frequently throughout the week, and limiting intake of salty snacks and processed foods. 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 phosphate and calcium resorption from bone. Foods with a preponderance of sulfur-containing amino acids (i.e., methionine and cysteine) contribute to higher dietary acid load. Highest on this list are animal protein, egg yolks, wheat protein isolates, wheat products, wheat-based baked goods, oats, barley, brown rice, and corn.143 Most nuts and seeds are mildly acidogenic as well. Although dairy products contain sulfur-containing amino acids that can contribute to acid production, milk and yogurt have a low or near-neutral potential renal acid load because their calcium, potassium, and magnesium contents partially offset the acid-generating effects of protein and phosphorus.144 Cheeses are the exception, particularly hard and aged cheeses, as they are lower in potassium and higher in phosphorus, thereby increasing their acidogenic potential. Protein needs vary greatly by age, gender, life stage, body habitus, and comorbidities. Accordingly, routine restriction of dietary protein to prevent kidney stones is not always appropriate and may be harmful to some individuals, particularly children. While the recommended dietary allowance (RDA) for protein in adults is 0.8 g/kg of body weight/day,145 older adults, individuals with chronic illness, those recovering from surgery or infection, and physically active patients often require more protein to preserve lean body mass, support immune function, and maintain physical function. Experts frequently recommend 1.0-1.2 g protein/kg of body weight/day for healthy older adults and 1.2-1.5 g protein/kg of body weight/day or more in those with chronic conditions.146 A systematic review concluded that higher protein intake, within the range of dietary reference intakes (DRIs), is consistent with normal kidney function in healthy individuals.147 However, it should be noted that there are many individuals who eat protein beyond the DRIs and never develop abnormal kidney function. Three RCTs evaluated the effect of lower animal protein intake, among other dietary recommendations, in preventing recurrent calcium stones (e.g., low salt, high fiber, normal calcium)27-29 and only one RCT was determined to provide sufficient evidence to support lower-protein recommendations.29 In that study, participants who limited protein from meats to no more than about 55% of total protein intake, consumed 3-4 servings of dairy daily, and ate less salt had lower stone recurrence rates than the control patients who were encouraged to maintain a high fluid intake only. Therefore, dietary recommendations for kidney stone prevention should emphasize appropriate protein quality and distribution within the context of overall nutritional adequacy rather than indiscriminate protein restriction.