Effect of carbohydrate ingestion during exercise on post-exercise substrate oxidation and energy intake.
Melby CL, Osterberg KL, Resch A, Davy B, Johnson S, Davy K.
Thirteen physically active, eumenorrheic, normal-weight (BMI < 25 kg/m2) females, aged 18-30 years, completed 4 experimental conditions, with the order based on a Latin Square Design: (a). CHO/Ex: moderate-intensity exercise (65% VO2peak) with a net energy cost of approximately 500 kcals, during which time the subject consumed a carbohydrate beverage (45 g CHO) at specific time intervals; (b). CHO/NoEx: a period of time identical to (a). but with subjects consuming the carbohydrate while sitting quietly rather than exercising; (c). NoCHO/Ex: same exercise protocol as condition (a.) during which time subjects consumed a non-caloric placebo beverage; and (d). NoCHO/NoEx: same as the no-exercise condition (b). but with subjects consuming a non-caloric placebo beverage. Energy expenditure, and fat and carbohydrate oxidation rates for the entire exercise/sitting period plus a 90-min recovery period were determined by continuous indirect calorimetry. Following recovery, subjects ate ad libitum amounts of food from a buffet and were asked to record dietary intake during the remainder of the day. Total fat oxidation (exercise plus recovery) was attenuated bycarbohydrate compared to placebo ingestion by only approximately 4.5 g. There was a trend (p =.08) for a carbohydrate effect on buffet energy intakesuch that the CHO/Ex and CHO/NoEx energy intakes were lower than the NoCHO/Ex and NoCHO/NoEx energy intakes, respectively (mean for CHO conditions: 683 kcal; NoCHO conditions: 777 kcal). Average total energy intake (buffet plus remainder of the day) was significantly lower (p <.05) following the conditions when carbohydrate was consumed (CHO/Ex = 1470 kcal; CHO/NoEx = 1285 kcal) compared to the noncaloric placebo (NoCHO/Ex =1767 kcal; NoCHO/NoEx = 1660 kcal). In conclusion, in young women engaging in regular exercise, ingestion of 45 g of carbohydrateduring exercise only modestly suppresses total fat oxidation during exercise. Furthermore, the ingestion of carbohydrate with or without exerciseresulted in a lower energy intake for the remainder of the day.