Whether you enjoy cardio or not, it’s a necessity for bodybuilders who want to significantly reduce body fat in a reasonable period of time. If the primary goal of doing cardio is to burn fat, as opposed to increasing aerobic endurance, one should perform cardio on an empty stomach. Insulin, which is the body’s primary storage hormone, reduces fat mobilization and oxidation. Insulin is higher after eating a meal. Thus, performing cardio while in a fasted state should lead to the highest level of fat oxidation.
Performing cardio in a fasted state will not lead to greater loss of body fat because the body will adapt, and if you burn more fat for fuel during a given time period, you will just burn more carbohydrates and less fat later in the day.
- Studies have shown that performing a single bout of exercise in the fasted states increases fat oxidation compared with the same exercise in a fed state.
- Research has shown that exercise can increase 24-hour fat oxidation but only if it is performed before eating the first meal of the day.
- A study looking at changes in body composition over the course of four weeks of training in a fasted and a fed state failed to show statistically significant differences between fed and fasted cardio.
- Though not statistically significant, the same study did show 60% greater fat loss in the fasted group compared with the fed group over four weeks, even though caloric intake was matched.
In general, doing your cardio on an empty stomach will enhance fat burning compared with cardio done after a meal.
Doing cardio before the first meal of the day, when insulin is lowest, reduces fat mobilization and oxidation. When you first begin your diet, do your cardio on an empty stomach if possible. Then, as you get closer to the show and your body fat is low, switch to doing cardio after a small meal in order to preserve muscle mass.