A Whole‐Grain Diet Increases Glucose‐Stimulated Insulin Secretion Independent of Gut Hormones in Adults at Risk for Type 2 Diabetes

Abstract

INTRODUCTION\nThe effect of whole-grain (WG) versus refined-grain (RG) diets on glucose-stimulated insulin secretion (GSIS) and β-cell function is unclear.\n\n\nMETHODS\nIn a double-blind crossover randomized controlled trial, 13 prediabetic adults (37.2\xa0±\xa01.8 y, BMI: 33.6\xa0±\xa01.4 kg m-2 , 2\xa0h glucose: 146.9\xa0±\xa011.6 mg dL-1 ) are provided isocaloric-matched WG and RG diets for 8-weeks each, with an 8-10 week washout between diets. Glucose, insulin, and C-peptide are studied over 240 min following a 75\xa0g OGTT. Incretins (GLP-1 and GIP), PYY, and total ghrelin are assessed at 0, 30, and 60 min. Mixed-meal diets for carbohydrate (54%), fat (28%), and protein (18%) contain either WG (50\xa0g/1000 kcal) or equivalent RG.\n\n\nRESULTS\nBoth diets induce fat loss (≈2 kg). While neither diet impacts early phase GSIS, the WG diet increases total GSIS (iAUC of C-peptide0-240 /Glc0-240 , p = 0.02) and β-cell function (disposition index; GSIS × insulin sensitivity, p = 0.02). GIP and PYY are unaltered by either diet, but GLP-1 is higher at 30 min following RG versus WG (p = 0.04). Ghrelin levels are higher at 60 min of the OGTT following both interventions (p = 0.01).\n\n\nCONCLUSION\nA WG-rich diet increases β-cell function independent of gut hormones in adults with prediabetes.