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The effects of fatty acids on gastrointestinal function and energy intake vary with their chain length. In rats, lauric acid, a fatty acid with 12 carbon atoms (“C12”) suppressed energy intake more than oleic acid, a fatty acid with 18 carbon atoms (“C18”), on a calorie-for-calorie basis. We hypothesised that, at equicaloric loads, C12 would inhibit antral pressure waves (PWs), stimulate pyloric pressure waves (IPPWs) and suppress appetite and energy intake more than C18. Ten healthy males were studied on three separate occasions. Pressure waves and appetite perceptions were measured during 60-min intraduodenal infusions of (i) C12, ii) C18 or iii) control (saline) (all pH 8.4, 0.4 kcal/min for C12 and C18). Energy intake was quantified at a cold buffet-style meal immediately following the infusions. Both C12 and C18 suppressed antral PWs and stimulated IPPWs compared with control (P

The effects of fat on gastric emptying, gastrointestinal hormone release and energy intake are dependent on the digestion of fat to free fatty acids (FFAs). There is limited information about the comparative effects of FFAs and triglycerides (TGs) on these factors. In animals, oleic acid inhibits energy intake more potently than an isocaloric infusion of its TG, triolein. Nine healthy males (23±2 years, BMI 22±1 kg/m 2 ) were studied on three occasions to evaluate the effects of (i) 40 g of oleic acid (“FFA”) (1830 kJ), (ii) 40 g of macadamia oil (“TG”) (1856 kJ) (both 600 ml oil-in-water emulsions stabilized with 4% milk protein and labelled with 15 MBq 123 I), or (iii) 600 ml 4% milk protein (“control”, 352 kJ), administered intragastrically, on gastric emptying, plasma CCK and PYY, appetite and energy intake. Gastric emptying of FFA was much slower than of TG ( P P P P P P Conclusion Free fatty acids empty from the stomach more slowly, but stimulate CCK and PYY release and suppress appetite and energy intake much more potently, than triglycerides.