Urine composition in normal subjects after oral ingestion of oxalate-rich foods.

1. Urinary composition was studied in nine healthy adults on unrestricted diet and low-oxalate diet with and without individual oxalate-rich foods. 2. Urine oxalate was constant on the low-oxalate and constant high-oxalate diets and only fluctuated greatly on unrestricted diet. 3. Urine oxalate was mainly due to dietary oxalate which accounts for up to two-thirds of urinary oxalate. 4. Urine oxalate was unaffected by urine volume. 5. Varying percentages of dietary oxalate were absorbed depending on the nature of the foodstuff. 6. Although tea was the main source of dietary oxalate in some people it, like strawberries, did not represent a real risk factor. Chocolates, peanuts, beetroot, rhubarb and spinach were considered as high-risk foods. 7. Calcium oxalate crystalluria at 4 degrees C was increased significantly when the oxalate-rich foods were taken. When urine was examined at 37 degrees C no increase in crystalluria was found.