Effects of glucose versus fructose ingestion on blood glucose concentration during rest and exercise

Ten healthy, nondiabetic male subjects (18-35 yrs.) ingested either fructose, glucose, or a sham solution in doseage of 0.75 gms/kg body weight, and were assigned to the rest or exercise group (80% VO₂ max for 30-min). Subjects participated in all six treatments which were: Fructose-Exercise (FE), Glucose-Exercise (GE), Control-Exercise (CE), Fructose-Rest (FR), Glucose-Rest (GR), and Control-Rest (CR). Blood samples were drawn immediately prior to ingestion, 30-min post ingestion (immediately prior to initiation of rest or exercise), and then at 10, 20, and 30 min into the rest or exercise bout. All samples were analyzed for glucose. Both GE and FE treatment initially elevated blood glucose levels (GE 57.0±9.8%, FE 25.0±6.5%). Once exercise was initiated following glucose ingestion, blood glucose declined very rapidly and ended below baseline (-5.1±6.5%). Following FE treatment, blood glucose declined initially in the first 10-min of exercise, but then increased significantly as exercise continued (25.3±13.3%). These results suggest, many of the frequently observed symptoms of fatigue related to hypoglycemia during endurance exercise events might be avoided with fructose ingestion prior to competition.