While obese stone formers have been demonstrated to have an increased risk of stone disease, analysis of whether dietary modifications improve urinary parameters has been lacking until recently. In a retrospective analysis of normal weight, overweight, obese, and super-obese patients, Torcelli et al. [8] evaluated 214 patients, and of those, 86 were obese or super obese. All patients received dietary recommendations that were individually modified and included increasing their oral intake of fluids (at least 2 l per day); decreasing salt in diet to less than 1,500 mg per day; decreasing animal protein intake, with a target of 0.8–1 g per kilogram per day; and increasing fruits rich in citric acid and/or potassium citrate. Patients with hyperoxaluria underwent a detailed inventory of items they may be eating that were high in oxalate and were counseled on calcium intake (1,200 mg per day) with meals. All groups of patients had improvements in urinary parameters on dietary modifications. In patients who were obese, there were significant improvements in all urinary parameters; in particular, urinary citrate level had the greatest improvement, increasing more than four times. Normal levels of 24-h urinary parameters were reached by greater than 50% of patients. Among super-obese patients, there were likewise significant improvements similar to the obese group [8].

Yun and colleagues investigated the effects of sodium restriction on stone disease recurrence and found that urine sodium significantly correlated with BMI, urine volume, pH, calcium, uric acid, oxalate, and citrate excretion. When controlling for BMI, stone formers with increased urinary sodium excretion had significantly higher urine volume, pH, calcium, uric acid, oxalate, citrate, and magnesium [29]. Individuals with decreased urinary sodium excretion were found to have fewer stone events, leading the authors to conclude that urinary sodium is associated with altered metabolite excretion in urine and with an increased risk of recurrent stone formation. Dietary sodium restriction should be considered the first conservative measure against recurrent stone formation [29].

The efficacy of dietary recommendations was also evaluated in patients after their initial stone event by Kocvara and colleagues. Patients were prospectively randomized to two groups, an intervention group in which specific dietary recommendations were made and reevaluated after repeat metabolic evaluation at 6, 18, and 36 months. In the control group, only general dietary recommendations were made, which included moderate animal protein intake, restricted oxalate consumption, increased dietary fiber intake, and decreased sodium and adequate calcium intake. Evaluation was carried out at 36 months. At 3 years of follow-up, there were significantly fewer recurrent stone events in the intervention group, where specific dietary recommendations were made as compared to the group that only received general dietary recommendations [31].

Specific dietary counseling has been shown to be beneficial in a separate investigation on dietary counseling and urinary stone parameters by Ortiz-Alvarado et al. [32]. The authors treated 137 patients with dietary modifications only to prevent stone recurrence. The patients were counseled to increase hydration to keeping urine volume above 2 l per day, sodium restriction to <2,400 mg per day, protein moderation to 3–4 oz twice per day, and adequate calcium intake (1,000–1,200 mg per day with meals), with an emphasis of timing with meals. Furthermore, citrate-containing juice, such as lemon juice, was advised. The investigators noted a significant improvement in urinary parameters, including decrease in urinary calcium, oxalate, and uric acid as well as increases in urinary citrate and volume with dietary modifications alone. These results further emphasize the importance of nutritional stone prevention as a first-line therapy.

In a recent Cochrane review of investigated dietary interventions aimed at preventing complications of idiopathic hypercalciuria , Escribano et al. found that diets that feature normal levels of calcium, low protein, and low sodium may reduce numbers of stone recurrences and decrease urinary oxalate excretion as well as reduce calcium oxalate supersaturation in idiopathic hypercalciuria with recurrent stone disease [33].

While many urologists support dietary recommendations as first-line therapy in the prevention of stone recurrence rates, due to time constraints, it is often difficult to obtain a full dietary history in all stone-forming patients. Interestingly, Wertheim and colleagues found that in a survey of endourologists regarding dietary counseling and stone disease, the majority urologists provide dietary recommendations for stone-forming patients, but most would like another provider to give recommendations likely due to time constraints [34]. This study points to an obvious issue with dietary counseling in stone-forming patients in that time plays a significant factor in how much education can be provided to patients in any one setting. Certainly utilizing nonphysician dietary specialists (e.g., registered dieticians) are essential in providing patient education and reinforcing dietary recommendations in the prevention of recurrent stone formation.