Dose-related effects of calcium to enhance the effects of L-tryptophan on gut hormones and energy intake in obesity.

Context: In males of normal weight, intraduodenal administration of calcium enhances the effects of the amino acid, L-tryptophan (Trp), to suppress energy intake, associated with greater stimulation of cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1) and peptide tyrosine-tyrosine (PYY) secretion (key mechanisms underlying the regulation of pyloric motility and gastric emptying), but not gastrin or glucose-dependent insulinotropic polypeptide (GIP).

Objective: Given the implications for the management of obesity, the current study evaluated the effects of calcium, when administered alone and in combination with Trp, on gut hormone secretion, antropyloroduodenal motility and energy intake in males with obesity.

Methods: Fifteen males with obesity and without type 2 diabetes (mean±SD; age: 27±8 years; body mass index: 30±2 kg/m2; HbA1c: 5.3±0.2%), received 150-min intraduodenal infusions of 0, 500 or 1000 mg calcium, each combined with Trp (load: 0.1 kcal/min, known to have submaximal energy intake-suppressant effects) from t=75-150 min, on three separate occasions, in a randomized, double-blind, cross-over order. Plasma concentrations of gastrin, CCK, GIP, GLP-1, PYY, and pyloric pressures were measured during the infusions. Immediately post-infusion (t=150-180 min), energy intake at a standardized buffet-style lunch was quantified.

Results: Calcium, in a dose of 1000 mg, stimulated GLP-1, PYY and pyloric pressures alone (all P<0.05), and enhanced the effects of Trp to stimulate CCK, GLP-1 and PYY (all P<0.05), associated with greater suppression of energy intake (P=0.01). Energy intake (R=-0.64; P=0.001) was inversely related to the dose of calcium, while plasma concentrations of CCK (R=0.44; P=0.05), GLP-1 (R=0.60; P=0.01) and PYY (R=0.83; P=0.01) were directly related.

Conclusions: Intraduodenal calcium enhances the effect of intraduodenal Trp to stimulate CCK, GLP-1 and PYY, and suppress energy intake, in males with obesity.