EFFECT OF DIETARY OXALATE AND CALCIUM ON URINARY OXALATE AND RISK OF FORMATION OF CALCIUM-OXALATE KIDNEY-STONES

Dietary restriction of oxalate intake has been used as therapy to redu ce the risk of recurrence of calcium oxalate kidney stones. Although u rinary oxalate is derived predominantly from endogenous synthesis, it may also be affected by dietary intake of oxalate and calcium. The ris k of increasing urinary oxalate excretion by excessive consumption of dietary oxalate is greatest in individuals with a high rate of oxalate absorption, both with and without overt intestinal disease. Although oxalate-rich foods enhanced excretion of urinary oxalate in normal vol unteers, the increase was not proportional to the oxalate content of t he food. Only eight foods-spinach, rhubarb, beets, nuts, chocolate, te a, wheat bran, and strawberries-caused a significant increase in urina ry oxalate excretion. Restriction of dietary calcium enhances oxalate absorption and excretion, whereas an increase in calcium intake may re duce urinary oxalate excretion by binding more oxalate in the gut. Thi s review of the literature indicates that initial dietary therapy for stone-forming individuals can be limited to the restriction of foods d efinitely shown to increase urinary oxalate. The effects of oxalate-re stricted diets on urinary oxalate should be evaluated by means of labo ratory analyses of urine composition. Subsequent long-term therapy can be recommended if beneficial results are obtained from oxalate restri ction at an appropriate calcium intake.