BACKGROUND & AIMS:Dietary fat intake is related to the degree of obesity, but the specific mechanisms by which fats regulate food intake in humans are unclear. We compared food intake suppression, plasma triglyceride appearance, and cholecystokinin (CCK) response after intestinal infusion of oils enriched with C18 fatty acids of increasing unsaturation. METHODS:Food intake and appetite changes after upper intestinal infusion of 0.9% saline, 20% Intralipid, and 20% emulsions of oils enriched with stearic, oleic, and linoleic acids were tested in 10 healthy male volunteers. Plasma triglyceride appearance and CCK release were tested separately in 7 additional volunteers. RESULTS:Intralipid and linoleic acid infusions significantly reduced food intake compared with saline infusion (P<0.05). No changes were observed in appetite ratings. There were no differences in plasma triglyceride response over the initial 75 minutes of intestinal infusion. Plasma CCK concentration increased after all lipid infusions (P<0.001), Intralipid infusion produced the highest increase in plasma CCK (P<0.05), and CCK response was similar between the 3 enriched oil emulsions. CONCLUSIONS:These results indicate marked differences in the ability of C18 fatty acids to reduce food intake that appear not to be related to rate of absorption but may partially be explained by CCK release.