Impact of pre-exercise rapid-acting insulin reductions on ketogenesis following running in Type 1 diabetes

P>Aim This study examined the effects of reductions to pre-exercise rapid-acting insulin dose on changes in blood beta-hydroxybutyrate, glucose, acid-base balance and counter-regulatory hormone responses to prolonged running in individuals with Type 1 diabetes. Methods Following ethical approval, seven participants with Type 1 diabetes (34 +/- 2 years, BMI 27 +/- 1 kg/m2) completed this study. After preliminary testing, participants attended the laboratory four times, each time consuming a 1.12MJ meal (60 g carbohydrate, 2 g fat, 2 g protein), with randomized amounts of their rapid-acting insulin: Full dose (mean 7.3 +/- 0.2 units), 75% dose (mean 5.4 +/- 0.1 units), 50% dose (mean 3.7 +/- 0.1 units) or 25% dose (mean 1.8 +/- 0.1 units). After 2-h rest, participants completed 45 min running at 70 +/- 1% peak rate of oxygen consumption (VO(2peak)). Blood metabolites and hormones were recorded over the 2-h rest and 3-h recovery. Data were analysed using repeated-measures ANOVA. Results Serum insulin peaked at 60 min in all conditions and was lowest after 25% insulin dose compared with full dose (P = 0.03). After the 25% insulin dose immediately pre-exercise glucose concentration was higher than after the full or 50% dose (P < 0.05). Resting beta-hydroxybutyrate gradually decreased during 2-h rest (P < 0.05) with a similar post-exercise peak of beta-hydroxybutyrate at 3 h (P > 0.05). Post-exercise blood pH increased for 5 min to a similar extent with all insulin doses , but the rise with the 25% dose was less compared with the full dose (P = 0.01). Blood lactate and plasma catecholamines increased after running similarly with all insulin reduction conditions (P < 0.05). Blood glucose area under the curve (BG(auc)) after the 25% insulin dose was greater than after the 75% dose (P = 0.02). Conclusion Ketogenesis following running was not influenced by reductions in pre-exercise rapid-acting insulin dose. This important preparatory strategy aids preservation of blood glucose but poses no greater risk to exercise-induced ketone body formation.