What is the role of diet in the formation of kidney stones?
The high animal protein (beef, poultry, pork, and fish) intake of many Americans (> 1.5–2 g/kg/day) acidifies the urine with phosphoric, sulfuric, and uric acids; decreases urinary citrate; increases urinary calcium; and raises the risk for nephrolithiasis. Higher protein diets, such as the Atkins diet, worsen these effects. Increased sulfates and uric acid may act as cofactors in the formation of calcium oxalate and uric acid stones. High sodium intake increases urinary calcium excretion (see question 15). High calcium intake (> 1500 mg) also contributes to hypercalciuria. However, low calcium intake (< 600 mg) without low oxalate intake decreases oxalate binding in the gut, increases oxalate absorption, and increases urinary oxalate. A diet high in protein and salt (sodium chloride [NaCl]) impairs citrate excretion by inducing subclinical intracellular and extracellular acidosis and increased reabsorption of citrate. Fructose adversely affects the microbiome, increases uric acid production, and increases the risk of nephrolithiasis. Diets high in calories and low in fiber, fruits, and vegetables are associated with obesity and increased nephrolithiasis. High dietary oxalate increases calcium oxalate crystalluria. Orange juice may help prevent kidney stones by increasing urinary potassium and citrate. Potassium citrate as Urocit-K is commonly prescribed to increase urinary citrate; if from Micromedex, Urocit-K at 60 mEq/day raises urinary citrate by approximately 400 mg/day and increases urinary pH by approximately 0.7 units. However, an 8-oz glass of orange juice supplies 12 mEq potassium and 38 mEq citrate (which is more compared with that supplied by a 10-mEq/1080-mg tablet of Urocit-K). Cranberry juice has mixed reviews, but data now suggest that it should not be used in excess in stone disease because it may increase urinary oxalate. Citric acid juices (lemon and lime) supply little potassium and only one third as much citrate as orange juice. Although potassium citrate juices are more powerful at stone inhibition, nearly all citrus drinks are useful. An exception is grapefruit juice, which may increase stone formation by 30% to 50%. The clinician should be flexible with the patient’s choice of fluid because the importance of the fluid intake may outweigh some of the theoretical negatives of the particular drink.
Selected High-Oxalate Foods
Adapted from Nelson, J. K., Moxness, K. E., Jensen, M. D., & Gastineau, C. F. (Eds.). (1994). Mayo Clinic Diet Manual (7th ed., pp. 315–362). St. Louis: Mosby.
|Vegetables||Leafy dark greens|