Postprandial glucose, insulin, and incretin responses to grain products in healthy subjects

Background: Various botanical and structural characteristics of starchy food modify the postprandial glucose and insulin responses in humans. Objective: We investigated what factors in grain products affect human glucose and insulin responses and elucidated the mediating mechanisms. Design: Ten men and 10 women [mean age: 28 +/- 1 y; mean body mass index (in kg/m(2)): 22.9 +/- 0.7] with normal glucose tolerance were recruited. The test products were whole-kernel rye bread, whole-meal rye bread containing oat beta-glucan concentrate, dark durum wheat pasta, and wheat bread made from white wheat flour. Paracetamol, a marker of the rate of gastric emptying, was added to the breads during baking. Each product provided 50 g available carbohydrate and was served in random order with breakfast (except for the beta-glucan rye bread, which was served at the last visit). Fasting and 8 postprandial blood samples were collected at intervals of 15-30 min for 3 h to determine plasma glucose, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP-1), serum insulin, and paracetamol concentrations. The in vitro starch hydrolysis, the structural characteristics (by light microscopy), and the molecular weight of beta-glucan in the test products were analyzed. Results: Glucose responses and the rate of gastric emptying after consumption of the 2 rye breads and pasta did not differ from those after consumption of white wheat bread. However, insulin, GIP, and GLP-1 responses, except for GLP-1 responses to the rye bread containing oat beta-glucan concentrate, were lower after the consumption of rye breads and pasta than after consumption of white wheat bread. Conclusions: Postprandial insulin responses to grain products are determined by the form of food and botanical structure rather than by the amount of fiber or the type of cereal in the food. These effects may be mediated through GIP and GLP-1.