A combined insulin reduction and carbohydrate feeding strategy 30 min before running best preserves blood glucose concentration after exercise through improved fuel oxidation in type 1 diabetes mellitus

In this study, we examined the glycaemic and fuel oxidation responses to alterations in the timing of a low glycaemic index carbohydrate and 75% reduced insulin dose, prior to running, in type 1 diabetes individuals. After carbohydrate (75 g isomaltulose) and insulin administration, the seven participants rested for 30 min, 60 min, 90 min or 120 min (conditions 30MIN, 60MIN, 90MIN, and 120MIN, respectively) before completing 45 min of running at 70% peak oxygen uptake. Carbohydrate and lipid oxidation rates were monitored during exercise and blood glucose and insulin were measured before and for 3 h after exercise. Data were analysed using repeated-measures analysis of variance. Pre-exercise blood glucose concentrations were lower for 30MIN compared with 120MIN (P < 0.05), but insulin concentrations were similar. Exercising carbohydrate and lipid oxidation rates were lower and greater, respectively, for 30MIN compared with 120MIN (P < 0.05). The drop in blood glucose during exercise was less for 30MIN (3.7 mmol · l−1, s[xbar] = 0.4) compared with 120MIN (6.4 mmol · l−1, s[xbar] = 0.3) (P = 0.02). For 60 min post-exercise, blood glucose concentrations were higher for 30MIN compared with 120MIN (P < 0.05). There were no cases of hypoglycaemia in the 30MIN condition, one case in the 60MIN condition, two in the 90MIN condition, and five in the 120MIN condition. In conclusion, a low glycaemic index carbohydrate and reduced insulin dose administered 30 min before running improves pre- and post-exercise blood glucose responses in type 1 diabetes