DIETARY OXALATE AND ITS INTESTINAL-ABSORPTION

Dietary oxalate is currently believed to make only a minor contributio n(< 20 %) to urinary oxalate excretion. A recent prospective study of stone disease suggested that dietary oxalate may be a significant risk factor. This observation led us to re-evaluate the contribution of di etary oxalate to urinary oxalate excretion. Previous studies have been hampered by inaccurate food composition tables for oxalate and inadeq uate methods for studying intestinal oxalate absorption. This evidence as well as factors that modify oxalate absorption are reviewed. New a pproaches to measure food oxalate and intestinal oxalate absorption ha ve been examined. Capillary electrophoresis appears to be well suited for the analysis of the oxalate content of food. Two individuals consu med an oxalate-free formula diet for 7 days. This diet decreased urina ry oxalate excretion by an average of 67 % (18.6 mg per 24 hours) comp ared to oxalate excretion on self-selected diets. The absence of detec table oxalate in feces by day 6 of the diet suggested that the intesti nal absorption was minimal. However, an effect of the formula diet on endogenous oxalate synthesis cannot be excluded. Restoring oxalate to the formula diet increased urinary oxalate excretion and illustrates t hat this experimental protocol may be well-suited for studying oxalate absorption and factors that modify it. Our results suggest that the i ntestinal absorption of dietary oxalate makes a substantial contributi on to urinary oxalate excretion and that this absorption can be modifi ed by decreasing oxalate intake or increasing the intakes of calcium, magnesium, and fiber.