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 ol estra ingestion on oxalate absorption and excretion. Seventeen healthy subj ects participated in three oxalate load (OL) tests separated by at least on e week and administered in the following order: OL-l, potato with fat (pota to chips) OL-2, potato with olestra (olestra-containing potato chips); and OL-3, potato without fat (boiled potatoes). The three experimental treatmen ts provided similar levels of carbohydrate. Oxalate loads, ingested immedia tely after consumption of the potato chips/boiled potatoes, consisted of 18 0 mg unlabeled oxalic acid and 14.3 mg C-13(2)-oxalic acid. Twenty-four hou r urine samples were collected the day before the OL tests and timed urine samples were collected during the 48 h post-oxalate ingestion period. Endog enously-derived oxalate did not differ between treatments. Oxalate absorpti on for OL-l (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. ( C) 1999 Elsevier Science Inc.