Detection of impaired intestinal absorption of long-chain fatty acids: validation studies of a novel test in a rat model of fat malabsorption

Background: Classic fat balance studies detect fat malabsorption but do not discriminate between the potential causes of malabsorption, such as impair ed intestinal lipolysis or reduced uptake of fatty acids. Objective: We aimed to validate a novel test for the specific, sensitive de tection of impaired intestinal uptake of long-chain unesterified fatty acid s in an appropriate rat model of fat malabsorption. Design: The absorption and appearance in plasma of [C-13]palmitic acid were determined in control rats and in rats with fat malabsorption due either t o chronic bile deficiency (permanent bile diversion) or to oral administrat ion of the lipase inhibitor orlistat (200 mg/kg diet). [C-13]Palmitic acid results were compared with the percentage absorption of ingested dietary fa t determined by fat balance. Results: Between 1 and 6 h after intraduodenal administration, plasma [C-13 ]palmitate concentrations in control rats were 4-10-fold higher than in bil e-deficient rats (P < 0.05) but were not significantly different between or listat-supplemented rats and their controls. In control and bile-deficient rats, plasma [C-13]palmitate concentrations allowed complete discrimination between normal (>92%) and reduced (<92%) fat absorption, whereas the perce ntage absorption of [C-13]palmitate over 48 h appeared to be highly correla ted with the percentage absorption of ingested dietary fat (r = 0.89, P < 0 .001). Conclusions: The [C-13]palmitic acid absorption test detects impaired intes tinal absorption of long-chain fatty acids selectively and sensitively in a rat model of fat malabsorption due to bile deficiency. Our data strongly s upport the use of the [C-13]palmitic acid absorption test for the diagnosis of clinical fat malabsorption syndromes.