CARBOHYDRATES LIMIT FAT METABOLISM
Kirwan et al. investigated the common practice of consuming carbohydrates in the form of grain products such as oatmeal before exercise in sports in terms of its effects on nutrient combustion and performance. In the fitness sector, the intake of complex carbohydrates from such foods is recommended in order to make training more effective and to endure exertion for longer.
6 Averagely well-trained subjects (3 men and 3 women) were given 75 g of carbohydrates in the form of oat flakes (corresponding to about 125 g of oat flakes) together with 300 ml of water 45 minutes before exercise; in a second test, however, only 300 ml of water were given to them. The subsequent sporting activity consisted of a bicycle ergometer exercise at 60% VO2max (corresponding to about 70% of the maximum heart rate) until subjective exhaustion.
IT WAS SHOWN THAT AFTER THE OATMEAL MEAL, IN THE FIRST 2 HOURS OF THE TEST, MORE CARBOHYDRATES WERE USED TO GENERATE ENERGY INSTEAD OF FATS. IF THE SUBJECTS WERE ONLY GIVEN WATER (THUS WERE SOBER), MORE FATS WERE BURNED.
Although the time for which the exercise was sustained tended to be higher after the oatmeal consumption at 254 minutes, this difference was not statistically significant compared to the 242 minutes of exercise duration after water consumption alone.
It can therefore be concluded that a significant improvement in endurance performance after a carbohydrate meal is rather unlikely. The increased burning of carbohydrates compared to fats, however, is to be viewed as negative from the perspective of fat metabolism-oriented training.
So if you do cardio training in the gym primarily to increase fat loss, SHOULD AVOID CARBOHYDRATE INTAKE BEFOREHAND. Especially since there does not seem to be any reduction in performance.