Fructose is as good a fuel as glucose for exercise in normal subjects

50 g fructose and 50 g glucose loads, naturally 13C labelled, were orally administered in random order to six healthy subjects submitted to 90 mn exercise at VO2 max/2 on a treadmill. 13CO2/12CO2 variations in the expired air were followed before and after exercise for a total of 240 min. On the whole, fructose appeared to be as good a fuel as glucose during exercise even if slight but significant differences in kinetics were observed: the delta 13C peak values at 90 min were significantly lower with fructose. Between 90 and 240 min, delta 13C remained higher but not significantly with 13C-fructose than with 13C-glucose. During exercise, plasma glucose and insulin levels were significantly lower (p less than 0.05 and p less than 0.01) after fructose than after glucose. We conclude that fructose can be readily used during exercise by healthy subjects.