Does Cardio on an Empty Stomach = Greater Calories Burned?

In college I’d wake up at the crack of dawn to meet my teammates for a run. Now, I can’t fathom doing that without any food (and caffeine) to get me going in the morning. And despite evidence to the contrary, many people still insist that exercise first thing in the morning in a fasted state will help them “burn more fat.”

There are a few reasons people vouch for this theorys. First, your blood sugar is low which means your insulin levels are low (insulin is a storage hormone and facilitates fat storage if you don’t need those calories for energy). Plus, some people believe that exercising first thing speeds up your metabolism for the rest of the day.

Despite these two seemingly logical theories behind exercising on an empty stomach first thing in the morning, my incredibly smart colleague Brad Schoenfeld, MS, CSCS, did an excellent job debunking this myth. In Brad’s article in the NSCA Strength & Conditioning Journal, he goes into depth discussing why this theory is incorrect. Here are the highlights:

  • Fat burning needs to be considered over the course of a day, actually days, not only during one exercise session. Say you burn carbs during your workout, then your body will likely burn fat post exercise or later in the day.
  • HIIT, high intensity interval training, has proven to be one of the best ways to shed fat. Yet, during this high intensity exercise, you are actually burning less fat which indicates that again, the whole day, or course of days matters the most.
  • Well designed clinical trials in endurance-trained athletes show that a pre-exercise meal does not impair fat oxidation during exercise.
  • If you exercise in a fasted state you probably won’t be able to train at the same intensity as you would if you had a pre-exercise meal. Greater intensity = more calories burned.

For all of the reasons outlined above, keep in mind that the best time of the day to exercise is the time that fits in your schedule and works for you. If you love to exercise first thing in the morning, go for it! Obviously it has it’s advantages since the rest of your day is free and you won’t skip out on an after-work workout in favor of a last minute happy hour. Plus, working out in the morning may get you “up” for the rest of your day, helping you feel like you’ve accomplished something and your body is both alert and ready to tackle anything that comes your way. However, don’t sweat it if you exercise in a non fasted state. After all, you should notice a huge difference in the quality of your workout.

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