Carbohydrate Requirements for Prolonged, Fasted Exercise with and without Basal Rate Reductions in Adults with Type 1 Diabetes on Continuous Subcutaneous Insulin Infusion (CSII)

Objective: Exercising while fasted in type 1 diabetes facilitates weight loss, however the best strategy to maintain glucose stability remains unclear.

Research Design and Methods: Fifteen adults on CSII completed three sessions of fasted walking (120min at 45%VO_2peak) in a randomized crossover design: 50% basal rate reduction set 90min pre-exercise (-90_min50%_BRR); usual basal rate with carbohydrate intake (0.3g/kg/hr; CHO-only); and combined 50% basal rate reduction set at exercise onset with carbohydrate (0.3g/kg/hr; Combo).

Results: Combo had a smaller change in glucose (5±47mg/dL) vs CHO-only (-49±61mg/dL, P=0.03) or -90_min50%_BRR (-34±45mg/dL). -90_min50%_BRR produced higher b-hydroxybutyrate levels (0.4±0.3 vs 0.1±0.1mmol/L) and greater fat oxidation (0.51±0.2 vs 0.39±0.1g/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.