Abstract
BackgroundThe rate of gastric emptying and glucoregulatory hormones are key determinants of postprandial glycaemia. Intragastric administration of L-tryptophan slows gastric emptying and reduces the glycaemic response to a nutrient drink in lean individuals and those with obesity. We investigated whether tryptophan decreases postprandial glycaemia and slows gastric emptying in type 2 diabetes (T2D).MethodsTwelve men with T2D (age: 63 ± 2 years, HbA1c: 49.7 ± 2.5 mmol/mol, BMI: 30 ± 1 kg/m2) received, on three separate occasions, 3 g (‘Trp-3’) or 1.5 g (‘Trp-1.5’) tryptophan, or control (0.9% saline), intragastrically, in randomised, double-blind fashion, 30 min before a mixed-nutrient drink (500 kcal, 74 g carbohydrates), containing 3 g 3-O-methyl-D-glucose (3-OMG) to assess glucose absorption. Venous blood samples were obtained at baseline, after tryptophan, and for 2 h post-drink for measurements of plasma glucose, C-peptide, glucagon and 3-OMG. Gastric emptying of the drink was quantified using two-dimensional ultrasound.ResultsTryptophan alone stimulated C-peptide (P = 0.002) and glucagon (P = 0.04), but did not affect fasting glucose. In response to the drink, Trp-3 lowered plasma glucose from t = 15–30 min and from t = 30–45 min compared with control and Trp-1.5, respectively (both P < 0.05), with no differences in peak glucose between treatments. Gastric emptying tended to be slower after Trp-3, but not Trp-1.5, than control (P = 0.06). Plasma C-peptide, glucagon and 3-OMG increased on all days, with no major differences between treatments.ConclusionsIn people with T2D, intragastric administration of 3 g tryptophan modestly slows gastric emptying, associated with a delayed rise, but not an overall lowering of, postprandial glucose.
Highlights
Gastric emptying and the release of the glucoregulatory hormones, insulin and glucagon, are important determinants of the postprandial blood glucose response to carbohydrate-containing meals, in health, obesity and type 2 diabetes (T2D)[1]
Study design We investigated the effects of intragastric administration of (i) 3 g (Trp-3) or (ii) 1.5 g (Trp-1.5) tryptophan, or (iii) control (0.9% saline) on plasma glucose, C-peptide, and glucagon concentrations and glucose absorption in response to, and gastric emptying of, a mixed-nutrient drink, consumed 30 min after the intragastric treatments
C-peptide and glucagon concentrations at t = −1 min, which we reported previously to correlate with subsequent glycaemic control[15], peak plasma glucose, time to peak glucose and gastric half-emptying time (T50) were analysed using repeated-measures analysis of variance (ANOVA)
Summary
Gastric emptying and the release of the glucoregulatory hormones, insulin and glucagon, are important determinants of the postprandial blood glucose response to carbohydrate-containing meals, in health, obesity and type 2 diabetes (T2D)[1]. In T2D, whey protein, when given as a preload 30 min before a high-carbohydrate meal, slowed gastric emptying and stimulated insulin, leading to a reduction in the glycaemic response[6]. These effects of protein appear to be mediated, at least in part, by their digestion products, amino acids — both circulating amino acids and as a result of the interaction of amino acids with the small intestine[7,8,9,10]. We investigated whether tryptophan decreases postprandial glycaemia and slows gastric emptying in type 2 diabetes (T2D)
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