Reference Glycaemic and Beta-Cell Profiles in Response to a Standardised Meal Challenge in Adults Across the Glycaemic Spectrum

Background: The pancreatic beta-cell hormone insulin regulates the metabolism of carbohydrates, as well as fats and protein. While the insulin response to a carbohydrate challenge is well defined in normoglycaemic as well as dysglycaemic (prediabetes and type 2 diabetes (T2DM)) individuals, the response of co-secreted beta-cell products (C-peptide, proinsulin and proinsulin intermediates) is less well defined. This analysis aimed to establish the expected glycaemic and pancreatic beta-cell responses to a standardised mixed meal in individuals with impaired glucose tolerance (IGT) and T2DM alongside reference ranges established in normoglycaemic individuals (NGT). Methods: A total of 743 adults (104 NGT, 85 IGT and 554 T2DM) were included, none of whom were on any anti-diabetic medication at the time of initial testing. All attended following a 10 h fast, before consuming a 500 kcal solid mixed meal (calorie contribution: 58% carbohydrates, 22% fat and 20% protein). Blood samples were collected every 30 min for the 4.5 h duration of the test for the determination of plasma glucose, insulin, C-peptide and intact and total proinsulin. Median profiles with corresponding 2.5th and 97.5th percentile lines to display the expected range were calculated and plotted for the three participant groups. Results: Median profiles with ranges over a 4.5 h meal period have been created for glucose, insulin, C-peptide and intact and total proinsulin, along with respective fasting and post-meal intervals in the three participant groups with differing glycaemic status. Conclusions: The resulting profiles and ranges allow for comparison in responses to a carbohydrate challenge in individuals across the glycaemic spectrum.