Circadian influences on glycemic control in 24-hr fasts initiated at different mealtimes

Introduction: This study investigated whether the timing of a 24-h fast influences indicators of glycemic control throughout the duration of the fast or upon refeeding. Methods: Twenty-four adults who have overweight or obesity (13 female, 11 male) completed this randomized crossover study involving three 24-h fasts initiated at either 8:00 am, 1:00 pm, or 6:00 pm followed by a 75 g oral glucose tolerance test (OGTT) which lasted 2 h. Continuous glucose monitors (CGMs) were employed to track interstitial glucose throughout each fast and OGTT. Plasma samples for insulin and glucagon were collected at the beginning and end of each fast, and 30 min post-OGTT. Capillary beta-hydroxybutyrate (BHB) was only measured at the end of the fasting. Results: > 0.05). Discussion: The timing of a 24-h fast alters glycemic control and metabolic switching. The afternoon fast optimized glycemic outcomes and ketosis, and these effects appear independent of insulin and glucagon. Aligning fasting protocols with circadian rhythms by initiating a 24-h fast in the afternoon may improve metabolic outcomes related to glycemic control during and immediately after the fast.