O'Hara, J. P., King, R. F., Carroll, S., & Cooke, C. B. (2010). The effects of pre-exercise galactose and glucose ingestion on fuel utilization during exercise using 13c-labeling. Presentation 858 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

This study determined the effect of ingesting galactose and glucose 30 minutes before exercise on fuel utilization during exercise. Well-trained male cyclists (N = 9) completed three rides at 60% Wmax for 120 minutes following the randomized pre-exercise ingestion (30 minutes before) of 75 g of galactose or glucose, labeled with either 13C galactose or 13C glucose, or placebo. Total carbohydrate and fat oxidation were computed from indirect calorimetry, every 15 minutes during exercise. Exogenous oxidation was calculated from expired air.

There were no significant differences between the three conditions in the absolute contributions of total carbohydrate or endogenous carbohydrate and fat during the exercise. However, exogenous glucose oxidation was significantly higher in comparison to galactose. The pre-exercise ingestion of glucose produced significantly higher mean and peak exogenous oxidation rates in comparison to galactose. Galactose produced a significantly higher range of exogenous oxidation rates during the last 30 minutes of exercise in comparison to glucose.

Implication. The pre-exercise consumption of glucose provides a higher mean exogenous source of carbohydrate during extended exercise, but galactose provides the predominant exogenous source of fuel during the latter stages.

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