Does High vs Low Glycemic Index Impact the Postprandial Glycaemic Response to Meals High in Protein and Fat in Adults with Type 1 Diabetes?

To determine the impact of a high glycaemic index (GI) carbohydrate vs a low GI carbohydrate in a meal high in carbohydrate, fat & protein on postprandial glycaemia in adults with type 1 diabetes. A randomised, within-subject trial comparing capillary postprandial glycaemia for a high GI white bread vs a low GI white bread served with 55g of peanut butter over 5h with the same insulin dose for all meals (based on the insulin: CHO ratio) in 12 adults with T1D using insulin pump therapy or multiple daily injections. Design Rationale For individuals with type 1 diabetes, currently the amount of carbohydrate in meals is the predominant factor that determines their meal time insulin dosage. However, recent research has shown that the amount of fat, protein and GI of meals can also impact the postprandial glycaemic response. This study will establish the relationship between GI and glycaemia for meals also high in protein and fat. Fat and protein will be added in the form of peanut butter. Test Meals & Insulin Doses Insulin doses calculated using participants’ insulin: CHO ratio (standard clinical practice). Test Meal 1: 2 slices of high GI toast (GI: 70) with 55g of peanut butter (35g CHO, 30g protein, 18g fat) Test Meal 2: 2 slices of low GI toast (GI: 52) with 55g of peanut butter (35g CHO, 30g protein, 18g fat) Wash out period: All test sessions must be completed on separate days but may be consecutive days. Study Procedure: Participants will be instructed to avoid alcohol and exercise for 24h prior to the session and not make any manual insulin adjustments (correction bolus or temporary basal rate) after midnight. Participants will be instructed to fast from midnight, with only water allowed. In the case of hypoglycaemia, participants will be instructed to treat their hypoglycaemia according to their usual clinical care and their test session will be rescheduled. Participants will be asked to attend the Clinical Research Facility for a screening appointment (approximately 30 minutes), to confirm eligibility, complete informed consent, provide instruction on the trial, provide test meals and commence the continuous glucose monitoring system (Abbott Freestyle Libre). Participants will be asked to complete the two test sessions at home within the next 14 days. The researchers will provide support and training through telephone or video conference. To ensure adherence to study protocol, participants' overnight and preprandial blood glucose level will be checked by researchers using CGM cloud data before the commencement of the test sessions. Also a case report form will be given to participants to ensure they fulfill all requirement (fasting and avoid exercises) the night before and during the test sessions. Test meals are weighted and supplied by research team. On the day of the test session, participants will be asked to start the session between 7:00-9:00am after an overnight fast. The fasting capillary blood glucose test must be between 4-10 mmol/L for the session to be commenced. The allocated insulin dose will be self-administered via insulin infusion through insulin pump into abdomen or subcutaneous injection into abdomen for people doing multiple daily injections. 15 minutes immediately prior to the consumption of the test meal. The test food will be served with 250mL of plain water and participants will be given 12 minutes to consume both the food and water and then no other food or drink allowed for the remainder of the 5h test session (except water). The CGM system will record the interstitial blood glucose level every 5 minutes throughout the test session. If hypoglycaemia occurs (> 3.5 mmol/L), the test session will be terminated, the event recorded and the participant treated appropriately.