Metabolic Effects of Glucose-Fructose Co-Ingestion Compared to Glucose Alone during Exercise in Type 1 Diabetes

This paper aims to compare the metabolic effects of glucose-fructose co-ingestion (GLUFRU) with glucose alone (GLU) in exercising individuals with type 1 diabetes mellitus. Fifteen male individuals with type 1 diabetes (HbA1c 7.0% +/- 0.6% (53 +/- 7 mmol/mol)) underwent a 90 min iso-energetic continuous cycling session at 50% VO2max while ingesting combined glucose-fructose (GLUFRU) or glucose alone (GLU) to maintain stable glycaemia without insulin adjustment. GLUFRU and GLU were labelled with C-13-fructose and C-13-glucose, respectively. Metabolic assessments included measurements of hormones and metabolites, substrate oxidation, and stable isotopes. Exogenous carbohydrate requirements to maintain stable glycaemia were comparable between GLUFRU and GLU (p = 0.46). Fat oxidation was significantly higher (5.2 +/- 0.2 vs. 2.6 +/- 1.2 mg center dot kg(-1)center dot min(-1), p < 0.001) and carbohydrate oxidation lower (18.1 +/- 0.8 vs. 24.5 +/- 0.8 mg center dot kg (-1)center dot min(-1) p < 0.001) in GLUFRU compared to GLU, with decreasedmuscle glycogen oxidation in GLUFRU(10.2 +/- 0.9 vs. 17.5 +/- 1.0mg center dot kg(-1)center dot min(-1), p < 0.001). Lactate levels were higher (2.2 +/- 0.2 vs. 1.8 +/- 0.1 mmol/L, p = 0.012) in GLUFRU, with comparable counter-regulatory hormones between GLUFRU and GLU (p > 0.05 for all). Glucose and insulin levels, and total glucose appearance and disappearance were comparable between interventions. Glucose-fructose co-ingestion may have a beneficial impact on fuel metabolism in exercising individuals with type 1 diabetes without insulin adjustment, by increasing fat oxidation whilst sparing glycogen.