Twenty-Five Hours of Fasting with Automated Insulin Delivery in Youth with Type 1 Diabetes

<b><i>Introduction and Objective:</i></b> Fasting presents unique metabolic challenges for individuals with T1D. The 25-h Yom Kippur complete fast provides an opportunity to evaluate whether automated insulin delivery (AID) systems can maintain metabolic stability, prevent hypoglycemia and ketosis, and determine basal insulin requirements during prolonged fasting. <b><i>Methods:</i></b> This real-world, noninterventional study included 54 adolescents and young adults with T1D (mean age 17.3 ± 3.3 years, HbA1c 6.8 ± 1.0%). Participants used MiniMed 780 G (<i>n</i> = 34), Control-IQ (<i>n</i> = 10), or open-source AID systems (<i>n</i> = 10). Common system-specific adjustments included setting a 150 mg/dL exercise target, activating sleep mode, and modifying basal or glucose targets, while 11 participants made no changes. Ketone levels were measured after the 25-h fast and a routine overnight fast. Analyses compared glucose and insulin across fasting periods and different 780 G settings and assessed predictors of hypoglycemia and ketone levels. <b><i>Results:</i></b> All participants successfully completed the fast. Mean TIR increased from 71.6 ± 13.9% during routine days to 82 ± 13.2% during fasting (<i>P</i> < 0.01), while time <70 mg/dL decreased from 2.6% to 2.2% (<i>P</i> = 0.017). Ten mild hypoglycemic events occurred after the pre-fast meal and one during fasting. A higher baseline percentage of time <70 mg/dL was the only predictor of hypoglycemia. No significant difference was found between 780 G users with exercise mode and those with no or minor changes. Participants received 43.4 ± 16.8% (range 9.3%-90%) of their usual insulin dose. Median (IQR) end-of-fast ketone levels were 0.4 (0.3, 0.7) mmol/L vs 0.1 (0, 0.1) mmol/L on a regular morning (<i>n</i> = 31); insulin doses <30% of usual dose were associated with higher ketone levels. No severe hypoglycemia or serious adverse events occurred. <b><i>Conclusion:</i></b> AID systems enable safe 25-h fasting by maintaining glucose control and reducing the risk of hypoglycemia and ketonuria. Fasting adjustments should be individualized and can often be minor.