The rate-limiting step to the oxidation of ingested carbohydrate is the rate at which it is absorbed from the intestine. Glucose is absorbed via SGLT-1 transporters with the rate of absorption determined by the number of transporters present. Animal studies have indicated that the number of transporters can be increased when dietary carbohydrate intake is increased and when the intestine is exposed to artificial sweeteners. Human studies have not observed any effect of this strategy on carbohydrate oxidation during relatively low intensity exercise. In this study, 10 healthy male and female participants (22±1 y; 69±12 kg; 176±10 cm) undertook two experimental trials involving 90 min of cycle exercise at an intensity of 70% heart rate reserve. In the two hours prior to exercise, participants ingested 400 mL of water (W) or 400 mL of water containing 159 mg of sucralose (S) in equal aliquots every 15 min. 500 mL of a commercially available sports drink, containing 75 mg of 13C glucose, was ingested before the start of exercise. Breath samples were collected at the start of each trial, before sports drink ingestion and at 15 min intervals throughout exercise and analysed for 13C:12C ratio. Average power output (W=148±26; S=140±36 watts) and heart rate (W=157±4; S=155±6 bpm) during exercise were similar (p>0.05) between trials. Delta Over Baseline (DOB) 13C:12C values showed a main effect of trial (p=0.016), time (p<0.001) and no interaction effect (p=0.242). DOB values were greater (p<0.05) during the sucralose trial 15 (W=7.7±4.2; S=11.4±5.6) and 60 (W=18.5±3.0; S=22.0±5.0) minutes after ingestion of the sports drink. The results of this study suggest some small differences in exogenous glucose oxidation during moderate intensity exercise when sucralose is ingested before exercise. This should be explored in greater detail with a longer pre-exercise supplementation period.
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