The consumption of energy drinks containing sucrose and caffeine is increasing worldwide. Ten healthy women aged 18 to 22 years and fasted overnight were randomly allocated to a standardised dose of sucrose either as an "energy" drink (containing sucrose and caffeine) or lemonade on the first day and then crossed over to the alternative drink on a second day. For thirty minutes before and thirty minutes after drinking oxygen consumption and carbon dioxide production were measured in the resting subject breath-by-breath by indirect calorimetry and the rates of carbohydrate and fat oxidation calculated. Energy drink consumption apparently caused increased carbohydrate oxidation (P = 0.004) and reduced lipid oxidation (P = 0.004) compared to lemonade. The longer term effects of combined caffeine and sucrose intake, particularly in sedentary individuals, on metabolism and body fatness needs further examination.