Fasted Cardio: Is There a Benefit?

Nov 19, 2013

Written by: Josh Sammons, Fitness Director, O2 Fitness - Chatham

Should I do my cardio workouts on an empty stomach?

As a personal trainer, I get this question quite a bit.

The Theory:

The idea behind doing cardio in the morning on an empty stomach is that the body's glucose levels are low after the nights fast.  Therefore, more fat should be used as the source of fuel as that is the default “secret” for improving fat loss.

The Truth:

With fasted cardio, however, your cortisol (muscle wasting hormone) is going to be very high. Being that you've consumed nothing anabolic, cortisol will lead to the use of amino acids for energy. Since you haven't taken any in, it's going to be stripped from your muscles. The actual research on fasted cardio does not demonstrate higher fat-loss results. Furthermore, the data showed that training in a fasted state actually impaired anabolism.

It CAN work, but:

In order for fasted cardio to have any kind of benefit to you, you will need to do steady state for about an hour or longer. Who has time for that?! Steady state cardio in this case is walking on a treadmill at the same pace with no incline. Compare 1 hour on a treadmill at speed 3.0 to 6-30 second sprints. You will burn double the calories in those 3 minutes than you did in the entire hour on the treadmill.

My conclusion: You will burn more fat over a 24 hour period when you eat before working out due to the greater thermogenic response to exercise.  Even more important than burning fat, with the correct diet and exercise program you will see results!

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