Gastric emptying of ingested fat emulsion in rats: implications for studies of fat-induced satiety

Evidence that ingested fat acts in the intestine to produce satiety stems from studies showing that intraintestinal infusion of fat emulsion inhibits eating behavior of rats. In this study, we determined the appropriateness of infusion parameters used in these behavioral studies by measuring gastric emptying rates of both the aqueous and lipid components of Intralipid ingested normally by rats. Stomach contents were collected at different times 0-40 min after rats ingested Intralipid containing [14C]polyethylene glycol (PEG) and phenol red (PR) and were assayed for PEG, PR, and fat. The proportion of ingested fat remaining in the stomach was significantly greater than the proportion of ingested PEG or PR at all time points examined. Despite initial gastric emptying of fat during ingestion, consumption of Intralipid (0.5 or 1.1 kcal/ml) did not suppress subsequent solid food intake. The results indicate that 1) ingested fat emulsion rapidly partitions in the rat stomach into an aqueous phase, which empties rapidly, and a lipid phase, which empties slowly, and 2) normal ingestion of Intralipid is not immediately satiating. These observations raise questions about the physiological significance of the rapid and marked suppression of feeding behavior produced by intraintestinal infusion of Intralipid.