Objectives: To assess the effects of a single dose of a non-absorbable fat substitute, sucrose polyester, on gastrointestinal function, Methods: The effects of 50 g of sucrose polyester taken as a single drink on gastric emptying, small bowel transit time (SBTT), whole gut transit time (WGTT) and faecal weight compared with a control fat were examined in double-blind studies. The effect of sucrose polyester on gallbladder ejection fraction and gastrointestinal hormones was also assessed, Results: Sucrose polyester was found to accelerate gastric emptying significantly (98.33 +/- 71.0 vs, 112.92 +/- 82.0 min, P = 0.042) but to slow SBTT (153.75 +/- 36.25 vs. 128.75 +/- 47.39 min, P = 0.006), A trend to faster WGTT (37.47 +/- 15.61 vs. 46.63 +/- 20.65 h) and increased faecal weight was observed (453.33 +/- 122.05 vs. 395.0 +/- 107.85 g/48 h), but this did not reach statistical significance, There was a striking reduction in gallbladder ejection fraction with sucrose polyester (21.69 +/- 25.32 vs. 45.27 +/- 27.67%), P = 0.039) and a corresponding significant decrease in the release of cholecystokinin, Lower levels of motilin and enteroglucagon were also observed. Conclusions: Sucrose polyester has significant effects on gastrointestinal transit, gallbladder contraction and gastrointestinal hormones, These effects can be explained on the basis of decreased luminal products of digestion and may have implications for the widespread use of sucrose polyester as a fat substitute.