Effects of intragastric administration of L-tryptophan on the glycaemic response to a nutrient drink in men with type 2 diabetes - impacts on gastric emptying, glucoregulatory hormones and glucose absorption

• Published in: Nutrition & diabetes Vol. 11; no. 1; pp. 3 - 9
• Main Authors: Hajishafiee, Maryam, Elovaris, Rachel A, Jones, Karen L, Heilbronn, Leonie K, Horowitz, Michael, Poppitt, Sally D, Feinle-Bisset, Christine
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 05.01.2021; Nature Publishing Group UK
• Subjects: 3-O-Methylglucose - blood; Aged; Beverages; Blood Glucose - drug effects; C-Peptide - blood; Diabetes; Diabetes Mellitus, Type 2 - blood; Diabetes Mellitus, Type 2 - drug therapy; Double-Blind Method; Drug Administration Routes; Gastric Emptying - drug effects; Glucagon; Glucagon - blood; Glucose; Glucose - metabolism; Humans; Insulin - blood; Intestinal Absorption; Male; Middle Aged; Nutrients; Obesity - drug therapy; Peptides; Postprandial Period; Tryptophan - administration & dosage
• DOI: 10.1038/s41387-020-00146-9
• ISSN: 2044-4052

The 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). Twelve men with T2D (age: 63 ± 2 years, HbA1c: 49.7 ± 2.5 mmol/mol, BMI: 30 ± 1 kg/m ) 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. Tryptophan 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. In 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.