Carbohydrate requirements for prolonged, fasted exercise with and without basal rate reductions in adults with type 1 diabetes on continuous subcutaneous insulin infusion

Abstract

OBJECTIVE Exercising while fasted with type 1 diabetes facilitates weight loss; however, the best strategy to maintain glucose stability remains unclear. RESEARCH DESIGN AND METHODS Fifteen adults on continuous subcutaneous insulin infusion completed three sessions of fasted walking (120 min at 45% VO2max) in a randomized crossover design: 50% basal rate reduction, set 90 min pre-exercise (290min50%BRR); usual basal rate with carbohydrate intake of 0.3 g/kg/h (CHO-only); and combined 50% basal rate reduction set at exercise onset with carbohydrate intake of 0.3 g/kg/h (Combo). RESULTS Combo had a smaller change in glucose (5 6 47 mg/dL) versus CHO-only (249 6 61 mg/dL, P 5 0.03) or 290min50%BRR (234 6 45 mg/dL). The 290min50%BRR strategy produced higher b-hydroxybutyrate levels (0.4 6 0.3 vs. 0.1 6 0.1 mmol/ L) and greater fat oxidation (0.51 6 0.2 vs. 0.39 6 0.1 g/min) than CHO-only (both P < 0.05). CONCLUSIONS All strategies examined produced stable glycemia for fasted exercise, but a 50% basal rate reduction, set 90 min pre-exercise, eliminates carbohydrate needs and enhances fat oxidation better than carbohydrate feeding with or without a basal rate reduction set at exercise onset.