Olestra and fat inhibit oxalate absorption

An experimental model which allowed a differentiation between endogenously-and exogenously-derived urinary oxalate was used to assess the effect of olestra ingestion on oxalate absorption and excretion. Seventeen healthy subjects participated in three oxalate load (OL) tests separated by at least one week and administered in the following order: OL-1, potato with fat (potato chips); OL-2, potato with olestra (olestra-containing potato chips); and OL-3, potato without fat (boiled potatoes). The three experimental treatments provided similar levels of carbohydrate. Oxalate loads, ingested immediately after consumption of the potato chips/boiled potatoes, consisted of 180 mg unlabeled oxalic acid and 14.3 mg ¹³C₂- oxalic acid. Twenty-four hour urine samples were collected the day before the OL tests and timed urine samples were collected during the 48 h post-oxalate ingestion period. Endogenously-derived oxalate did not differ between treatments. Oxalate absorption for OL-1 (10.5 %) and OL-2 (10.2 %) was lower (P<0.05) than for OL-3 (13.2 %). The presence of fat or olestra depresses total oxalate absorption.