Fasted Cardio

Fasted Cardio

If you ever want to start an argument among fitness enthusiasts, bring up fasted cardio. Old school bodybuilders are generally outspoken supporters of fasted cardio. And there is even some debate among well known fitness writers. Others claim that the negatives of fasted cardio outweigh the positives and that any fasted training is a broscience relic from the bodybuilding days of old. Which side is right? Read on to find out.

Years ago, when I competed in my first bodybuilding competition, it was understood by pretty much everyone that fasted cardio was almost a requirement for getting lean. The thought was that by doing cardio immediately after waking and before consuming any food, you would burn more fat because, well, there wasn't any other available energy to burn. This thinking was further popularized in Bill Phillips's book Body For Life [1].

If you are concerned with burning fat during the exercise, then fasted cardio may well be a good choice. However, a person's fat loss goals typically last longer than just a single cardio session. And since that is the case, it doesn't really matter how much fat you may or may not burn during a single cardio session. What matters is your net daily/weekly energy expenditure.

Maximizing Performance is Maximizing Fat Loss

The goal of cardio should therefore not be maximizing fat loss during exercise, but maximizing energy expenditure during exercise and throughout the day/week. Fasted cardio actually works against that goal. Training in a fasted state actually reduces intensity and maximum output [2][3].

It’s not surprising that some level of performance is sacrificed when training in a fasted state. Also, not surprisingly, performance and energy expenditure go hand in hand. Not only that, research has shown that higher intensity cardio (i.e. HIIT) can increase the total number of calories burned during the day, which in turn can increase fox oxidation for the day [4]. So, if high intensity cardio is more effective for burning fat over the duration of a day and fasted cardio reduces intensity and performance... I think you can get where this is going.

#1 Goal Of Fat Loss: Preserving Muscle

If you want to get lean then a big goal of any diet/training program targeted at fat loss should be preserving muscle. In fact, I believe the number one goal of any diet/training program targeted at fat loss should be preserving muscle. After all, what good does it do to shed a bunch of fat if you're shedding muscle at the same time? And aside from lower energy output, fasted cardio makes you more susceptible to muscle loss [3].

To Fasted Cardio or To Not Fasted Cardio?

Fasted cardio decreases your energy output by inhibiting performance and it can increase muscle loss. And although it may increase fat burned during exercise, it does not increase fat oxidation over the duration of a day. In my opinion, that's a pretty good case for not integrating fasted cardio into my training regimen, even when trying to lose fat. It looks like the research is in and for me, fasted cardio is out.

References

[1] Phillips, Bill, et al. Body for life. HarperCollins, 1999.


[2] Schabort, ELSKE J., et al. "The effect of a preexercise meal on time to fatigue during prolonged cycling exercise." Medicine and science in sports and exercise 31.3 (1999): 464-471.

[3] Schoenfeld, Brad. "Does Cardio After an Overnight Fast Maximize Fat Loss?." Strength & Conditioning Journal 33.1 (2011): 23-25.

[4] Tremblay, Angelo, Jean-Aimé Simoneau, and Claude Bouchard. "Impact of exercise intensity on body fatness and skeletal muscle metabolism." Metabolism 43.7 (1994): 814-818.

Posted by Clayton Long