Abstract
Tryptophan stimulates plasma cholecystokinin and pyloric pressures, both of which slow gastric emptying. Gastric emptying regulates postprandial blood glucose. Tryptophan has been reported to decrease energy intake. We investigated the effects of intragastric tryptophan on the glycaemic response to, and gastric emptying of, a mixed-nutrient drink, and subsequent energy intake. Lean and obese participants (n = 16 each) received intragastric infusions of 1.5 g (“Trp-1.5g”) or 3.0 g (“Trp-3.0g”) tryptophan, or control, and 15 min later consumed a mixed-nutrient drink (56 g carbohydrates). Gastric emptying (13C-acetate breath-test), blood glucose, plasma C-peptide, glucagon, cholecystokinin and tryptophan concentrations were measured (t = 0–60 min). Energy intake was assessed between t = 60–90 min. In lean individuals, Trp-3.0g, but not Trp-1.5g, slowed gastric emptying, reduced C-peptideAUC and increased glucagonAUC (all P < 0.05), but did not significantly decrease the blood glucose response to the drink, stimulate cholecystokinin or reduce mean energy intake, compared with control. In obese individuals, Trp-3.0g, but not Trp-1.5g, tended to slow gastric emptying (P = 0.091), did not affect C-peptideAUC, increased glucagonAUC (P < 0.001) and lowered blood glucose at t = 30 min (P < 0.05), and did not affect cholecystokinin or mean energy intake. In obese individuals, intragastrically administered tryptophan may reduce postprandial blood glucose by slowing gastric emptying; the lack of effect on mean energy intake requires further investigation.
Highlights
The slowing of gastric emptying and the release of gut and pancreatic hormones both play important roles in the regulation of food intake and postprandial blood glucose
We have reported that intraduodenal infusion of tryptophan at doses of ~0.41–3.3 g stimulates pyloric pressures, a key regulator of gastric emptying, in lean and overweight volunteers [12,15] and increases plasma CCK and glucagon concentrations [12]
The aims of this study were, to investigate the effects of intragastric tryptophan, at doses of 1.5 g or 3.0 g, based on previous studies [12,14,17], on the blood glucose response to and gastric emptying of a mixed-nutrient drink and subsequent energy intake in lean and obese volunteers
Summary
The slowing of gastric emptying and the release of gut and pancreatic hormones both play important roles in the regulation of food intake and postprandial blood glucose. Specific nutrients may potently activate gastrointestinal (GI) functions that are involved in the regulation of blood glucose and/or energy intake. We have reported that intraduodenal infusion of tryptophan at doses of ~0.41–3.3 g stimulates pyloric pressures, a key regulator of gastric emptying, in lean and overweight volunteers [12,15] and increases plasma CCK and glucagon concentrations [12]. When ingested orally in capsules (dose: ~3 g) 45 min before a lunch meal, or administered intraduodenally over 90 min (dose ~3.3 g), tryptophan markedly decreased energy intake in healthy subjects [12,17]
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