A 32-year-old man comes to the office for evaluation after a recent visit to the emergency department due to recurrent nephrolithiasis. The patient passed the stone spontaneously with supportive care alone. Analysis of the stone composition later revealed calcium oxalate crystals. The patient drinks 1 or 2 beers daily but does not use tobacco or illicit drugs. His diet consists of mostly processed foods and meats obtained at local stores, and he avoids fruits, vegetables, and dairy products.
Vital signs are within normal parameters. BMI is 32 kg/m². Physical examination is normal. Serum chemistry is normal. You provide affirmation of his desire to lose weight and recommend increasing his water intake.
In addition to weight loss and increased fluid intake, which of the following is the best dietary recommendation to reduce the risk of recurrent nephrolithiasis in this patient?

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Quizplus · Accepted Answer

11ec193a_990e_bce9_853d_c7cb802955db_MD0002_00 Nephrolithiasis occurs when supersaturated metabolites crystallize in the urine. Approximately 75% of kidney stones are calcium based (primarily calcium oxalate), and up to 50% of patients develop recurrent stones within 5 years. Dietary modifications can reduce the risk of stone formation, primarily by reducing urinary calcium and oxalate. In the past, patients were counseled to avoid calcium, but high dietary calcium intake actually decreases the risk of stone formation. Dietary calcium binds oxalate within the gastrointestinal tract, thereby decreasing systemic absorption of oxalate and subsequent excretion into the urine. However, supplemental (vs dietary) calcium may actually raise the risk of stone formation. If patients have recurrent stones despite dietary measures, medications (eg, thiazide diuretics, potassium citrate, allopurinol) may be needed to alter urine composition. (Choice A) Cranberry juice is often promoted to reduce the risk of urinary tract infections. However, its effect on the formation of calcium oxalate stones is unclear. Increasing dietary calcium is a better option to decrease the risk of stone formation. (Choice B) Despite prior recommendations, coffee, tea, and alcohol actually decrease the risk of calcium stone formation through their inhibition of antidiuretic hormone, leading to increased urine volume and decreased concentration of solutes (eg, calcium, oxalate). (Choice C) Reduction of high purine-containing foods (eg, seafood, organ meats) decreases uric acid production and is recommended for patients with uric acid stones, not calcium stones. (Choice E) Calcium is passively reabsorbed in the proximal tubule following sodium and water reabsorption. High sodium intake decreases proximal tubule sodium reabsorption and leads to increased urinary calcium levels, thereby raising the risk of calcium stone development. Educational objective: Calcium oxalate stones are the most common cause of nephrolithiasis. To reduce the risk of recurrent nephrolithiasis, patients should increase intake of fluids, dietary calcium, and fruits and vegetables, and decrease intake of sodium and animal protein. __________

A 32-Year-Old Man Comes to the Office for Evaluation After