The fatty acid, lauric acid (C12), and the amino acid, leucine (Leu) stimulate gut hormones, including CCK, associated with suppression of energy intake. In our recent study, intraduodenal infusion of a combination of C12 and l-tryptophan, at loads that individually did not affect energy intake, reduced energy intake substantially, associated with much greater stimulation of CCK. We have now investigated whether combined administration of C12 and Leu would enhance the intake-suppressant effects of each nutrient, when given at loads that each suppress energy intake individually. Sixteen healthy, lean males (age: 23 ± 2 yr) received, in randomized, double-blind fashion, 90-min intraduodenal infusions of control (saline), C12 (0.4 kcal/min), Leu (0.45 kcal/min), or C12+Leu (0.85 kcal/min). Antropyloroduodenal pressures were measured continuously and plasma CCK at 15-min intervals, and energy intake from a standardized buffet-meal, consumed immediately postinfusion, was quantified. All nutrient infusions stimulated plasma CCK compared with control (P < 0.05). Moreover, C12 and C12+Leu stimulated CCK compared with Leu (P < 0.05) (mean concentration, pmol/L; control: 2.3 ± 0.3, C12: 3.8 ± 0.3, Leu: 2.7 ± 0.3, and C12+Leu: 4.0 ± 0.4). C12+Leu, but not C12 or Leu, stimulated pyloric pressures (P < 0.05). C12+Leu and C12 reduced energy intake (P < 0.05), and there was a trend for Leu to reduce (P = 0.06) energy intake compared with control, with no differences between the three nutrient treatments (kcal; control: 1398 ± 84, C12: 1226 ± 80, Leu: 1260 ± 92, and C12+Leu: 1208 ± 83). In conclusion, combination of C12 and Leu, at the loads given, did not reduce energy intake beyond their individual effects, possibly because maximal effects had been evoked.
Keywords: branched chain amino acid; fatty acid; food intake; gastrointestinal functions; humans.