Inclusion/exclusion criteria Participants: For inclusion in the study, volunteers will be either male or female and aged 18-50 years old, free from any diabetes complications apart from background diabetic retinopathy, not taking any prescribed medication other than insulin, and be treated with a stable insulin regimen composed of a combination of slow/long acting insulin glargine/determir and a fast acting insulin analogue (lispro or aspart, glulisine), and have a HbA1c of <9.5% (80 mmol/mol). Participants will be currently using the carbohydrate counting method for administering meal time rapid-acting insulin.