A patient is passing stones recurrently in urine for past few years. All are due to be restricted in diet except

Calcium restriction Calcium intake in stone Higher urine calcium is a common finding in stone formers, but restricting dietary calcium intake is not recommended unless it is excessive (more than 2000 mg/d). Although urine calcium excretion may decrease with restriction, the decrease in free intestinal calcium can lead to increased absorption of dietary oxalate and enhanced oxalate excretion, due to decreased binding of oxalate by calcium in the intestinal lumen. The net effect may be increased supersaturation of the urine with respect to calcium oxalate and an enhanced tendency to stone formation. Prevention of recurrent calcium stones (which are usually composed primarily of calcium oxalate) is aimed at decreasing the concentrations of the lithogenic factors (calcium and oxalate) and at increasing the concentrations of inhibitors of stone formation, such as citrate. - Achieving these goals may require both dietary modification and the administration of appropriate medications. Medical therapy (and metabolic evaluation) is usually undeaken in individuals who have formed more than one stone. Reduce animal protein intake Adverse changes in urinary calcium and citrate excretion can be induced by a high protein diet, since the metabolism of sulfur- containing amino acids increases the daily acid load by generating sulfuric acid. Animal protein is much more likely to induce this effect than vegetable protein, since it has a higher sulfur content and therefore generates more acid. Thus, lowering animal protein intake will produce ,orable changes in the urine. However, it has not been proven that this will reduce the incidence of stone .formation. In observational studies, a high animal protein diet was a risk factor.for renal stones in men, but not in women. In a randomized trial, reduced animal protein in association with higher dietary calcium and lower dietary sodium was associated with a reduced risk of stone recurrence, but the individual impact of animal protein could not be determined. Based on the available data, it would be prudent to avoid excessive animal protein intake. Increase fruit and vegetable intake Foods that are rich in potassium, paicularly fruits and vegetables, may be beneficial. Increasing intake of fruits and vegetables may reduce the risk of calcium oxalate stone formation, paicularly in patients who self-select a diet that is low in fruits and vegetables. This benefit is primarily the result of increasing citrate excretion. Limit dietary oxalate intake Some .foods contain very large amounts of oxalate and those should be avoided (eg spinach, rhubarb). In addition, some nuts and legumes are also high in oxalate and the intake should be limited (eg, peanuts, cashews, and almonds). However, there is scant evidence that low oxalate diets reduce the risk of stone formation. In prospective observational studies of individuals who had never had a stone, higher dietary oxalate only slightly increased the risk of incident stone formation in men and older women; there was no association in younger women. Because of the documented health benefits of many .foods that are traditionally considered high in oxalate (but still 10 mg or less per serving), strict oxalate restriction does not seem to be suppoed. As noted above, some foods traditionally believed to be high in oxalate, such as tea, do not increase the risk of stone formation. If a low oxalate diet is recommended, it should only be continued if there is documented evidence that the urine oxalate excretion has fallen. Limit sodium intake Calcium is reabsorbed passively in the proximal tubule down the .orable concentration gradient created by the reabsorption of sodium and water. Thus, a low sodium diet (to 80 to 100 meq/day) can enhance proximal sodium and calcium reabsorption, leading to a reduction in calcium excretion. In one study, for example, lowering sodium intake from 200 to 80 meq/day diminished calcium excretion by as much as 100 mg/day (2.5 mmol/day). Although the independent contribution of lowering dietary sodium intake on actual stone formation is unknown and higher sodium intake may be associated with higher urine volume, it is likely an impoant component of a regimen that has been demonstrated to reduce recurrent stone .formation. Limit sucrose and fructose intake Sucrose intake increases urine calcium independent of calcium intake and has been associated with an increased risk of stones. Fructose intake also increases the risk of stone .formation. Calcium intake Higher urine calcium is a common finding in stone forrners, but restricting dietary calcium intake is not recommended unless it is excessive (more than 2000 rued). Although urine calcium excretion may decrease with restriction, the decrease in .free intestinal calcium can lead to increased absorption of dietary oxalate and enhanced oxalate excretion, due to decreased binding of oxalate by calcium in the intestinal lumen. The net effect may be increased supersaturation of the urine with respect to calcium oxalate and an enhanced tendency to stone .formation. The ability to help prevent new stone formation with a normal calcium intake was shown in pa by a five year study that compared two diets among men with idiopathic hypercalciuria and recurrent calcium oxalate stones. - In this trial, 120 such men were randomly assigned to either a diet consisting of a normal amount of calcium (1200 mg/day ) and low amounts of animal protein (52 g/day) and salt (2900 mg/day of sodium chloride) or a diet containing a low amount of calcium (400 mg/day ). At .five years, a significantly lower risk of stone recurrence was observed among the group assigned to the normal calcium, low animal-protein, low-salt diet. - This selective benefit likely arose because of a decrease in urinary oxalate excretion compared to an increase with the low calcium diet; the urine calcium actually decreased in both treatment arms. However, the independent effect of calcium is unclear given that the amounts of animal protein and salt ingested among those in the low calcium diet differed from that of patients in the normal calcium diet group. Nonetheless, the low calcium intervention was not beneficial and is not recommended. -In addition to increasing stone formation, a low calcium diet may have a second deleterious effect in patients with idiopathic hypercalciuria: development of negative calcium balance. This extra loss of calcium can exacerbate the already diminished hone density in some of these patients, a complication that may be due to enhanced bone resorption. It should be noted that calcium supplements do not appear to be effective in preventing recurrent stones and may even slightly increase risk. - Ira patients with a history of stones who require calcium supplements (eg, .for the treatment of osteoporosis), a suggested approach is to measure urinary calcium excretion before and approximately one month after staing the calcium supplement. If there is a clinically impoant increase in urinary calcium excretion, then the addition of a thiazide diuretic may be useful to reduce urinary calcium excretion (and to help maintain bone density). Other factors High dose vitamin C appears to increases urine oxalate excretion in ceain individuals and the risk of stone .formation; thus, high dose supplements should be avoided in those with higher urine oxalate excretion. Phytate appears to decrease the risk of stones in women. Although not simply a matter of dietary intake, higher body mass index increases the risk of stone .formation, paicularly in women. Therefore, weight control may be helpful in preventing stone recurrence. Nothing has been mentioned about dietary phosphate restriction. - Most of the urinary phosphate is derived from dietary protein. - Dietary protein restriction results in decrease in phosphate in urine. Increase intake offluid - To reach this goal, the best strategy is to reconmzend how much additional fluid the patient should drink based on his or her 24 hour urine volume. As an example, if the total urine volume is 1.5 liters, then we recommend two additional 8 ounce (240 mL) glasses of .fluid each day to reach the goal of at least 2 liters of urine output per day. Limiting animal protein in the diet - Although it has not been proven that a low protein diet will reduce the incidence of stone formation, a high animal protein diet is a risk factor for renal stones in men, but not in women. Limiting dietary sodium to 100 meq/day - A low sodium diet can enhance proximal sodium and calcium reabsorption, leading to a reduction in calcium excretion. Increasing dietary potassium intake - As this substantially decreases risk in men and older women. Limiting dietary sucrose and fructose Limiting dietary oxalate and vitamin C in patients with calcium oxalate stones. - However, excessive limitation is not likely to be helpful; patients should continue to consume a wide variety of fruits and vegetables.