Effects of intraduodenal administration of lauric acid and L-tryptophan, alone and combined, on gut hormones, pyloric pressures, and energy intake in healthy men

Background: The fatty acid, lauric acid ('C12'), and the amino acid, L-tryptophan ('Trp'), modulate gastrointestinal functions including gut hormones and pyloric pressures, which are important for the regulation of energy intake, and both potently suppress energy intake. Objective: We hypothesized that the intraduodenal administration of C12 and Trp, at loads that do not affect energy intake individually, when combined will reduce energy intake, which is associated with greater modulation of gut hormones and pyloric pressures. Design: Sixteen healthy, lean males (age: 24 +/- 1.5 y) received 90-min intraduodenal infusions of saline (control), C12 (0.3 kcal/min), Trp (0.1 kcal/min), or C12 + Trp (0.4 kcal/min), in a randomized, double-blind, cross-over study. Antropyloroduodenal pressures were measured continuously, and plasma cholecystokinin (CCK), ghrelin, and glucagon-like peptide-1 (GLP-1) concentrations, appetite perceptions, and gastrointestinal symptoms at 15-min intervals. Immediately after the infusions, energy intake from a standardized buffet meal was quantified. Results: C12 + Trp markedly reduced energy intake (kcal; control: 1,232 +/- 72, C12: 1,180 +/- 82, Trp: 1,269 +/- 73, C12 + Trp: 1,056 +/- 106), stimulated plasma CCK (AUC(area under the curve) 0-90 min, pmol/L*min; control: 21 +/- 8; C12: 129 +/- 15; Trp: 97 +/- 16; C12 + Trp: 229 +/- 22) and GLP-1 (AUC(0-90 min), pmol/L*min; control: 102 +/- 41; C12: 522 +/- 102; Trp: 198 +/- 63; C12 + Trp: 545 +/- 138), and suppressed ghrelin (AUC(0-90 min), pg/mL*min; control: -3,433 +/- 2,647; C12: -11,825 +/- 3,521; Trp: -8,417 +/- 3,734; C12 + Trp: -18,188 +/- 4,165) concentrations, but did not stimulate tonic, or phasic, pyloric pressures, compared with the control (all P < 0.05), or have adverse effects. C12 and Trp each stimulated CCK (P < 0.05), but to a lesser degree than C12 + Trp, and did not suppress energy intake or ghrelin. C12, but not Trp, stimulated GLP-1 (P< 0.05) and phasic pyloric pressures (P< 0.05), compared with the control. Conclusion: The combined intraduodenal administration of C12 and Trp, at loads that individually do not affect energy intake, substantially reduces energy intake, which is associated with a marked stimulation of CCK and suppression of ghrelin. The study was registered as a clinical trial at the Australian and New Zealand Clinical Trial Registry (www.anzctr.org.au,) as 12613000899741.