Does Fasted Cardio Really Work?

Feb 3, 2017

 by Stephen Conca

Fasted Aerobic Training or Referred To As Fasted Cardio?

The idea behind fasted cardio is that you should wake up, not have breakfast, not eat anything at all, grab your water and hit the cardio equipment. Trainers and coaches will tell you that performing low intensity training fasted (no food before session) will speed up fat loss. If any coach or trainer tells you this, run. If steady state aerobic exercise does very little for fat loss then how is doing it without eating going to change anything? Because I would really like to know, but then again I'm not a fitness guru. The whole premise of fasted cardio stems from the belief that there is this mythical fat burning zone.

Fat Burning Zone On Trial

Studies have shown over the years that the percent of calories burned during exercise come from glycogen and from fat stores. The relative contribution of the two sources changes according to exercise intensity. Peak fat oxidation has been shown to occur during exercise at about 63% of our VO2 max. The higher this percentage got, the smaller that fat oxidation window became. Working out at 87% of VO2 max is near the lactate threshold. Basically the harder we exercise, the less fat we are going to use as energy. After these studies were released, people thought that lower intensity cardio was the end all be all to fat loss protocols. But we must note that even though higher intensity work may burn fewer calories as a percentage, it stills burns more total calories. Total fat and calories burned overall (the 23 hours of the rest of the day following your session) is significantly higher in high intensity work. For real world fat loss, the research and evidence leads us to believe that high intensity cardio is the way to go!

Fasted Cardio Examined

The research shows that subjects consistently experience a greater thermic effect post exercise in both low and high intensity ranges. This just means that the total caloric burn was higher in subjects who had eaten prior to exercise. It has been shown that carbohydrate ingestion during moderate-intensity (65-75% VO2max) does not reduce fat oxidation during the first 120 min of exercise in trained males.

Researchers conducted a study comparing a fast group and a group give a glucose and milk mixture prior to exercise. The also compared high intensity short duration cardio training with low intensity long duration training. Results suggest that pre-exercise intake of carbohydrates increase EPOC (Excess Post Exercise Oxygen Consumption) above that of the fasting group, and high intensity short duration exercise increases fat oxidation during recovery period more than low intensity long duration exercise. To summarize these findings, the research does show that at low intensities (below 50% of VO2max) carbohydrate ingestion does reduce fat oxidation in untrained subjects. However, these studies did not look at fat oxidation beyond the exercise period.

At moderate intensities carbohydrates during exercise will not reduce fat oxidation in trained subjects for at least the first 80-120 minutes of exercise. At the peak level of fat oxidation (~63% of VO2max), carbohydrate increases performance without any suppression of fat oxidation in trained subjects. So basically fasted cardio provides no benefit at all when compared to cardio done after eating.

Here's a stupid statement:

Training for fat loss is the same as training for weight gain. The training doesn't change – just your diet.

The same trainers that say this are the same that recommend low rep training for strength, hypertrophy, speed training and fat loss training. These trainers use the same program for practically everyone, this can be compared to a doctor prescribing the same drug regardless of the condition. If the training does not change because of your goals (fat loss as opposed to strength training, or hypertrophy), then when would we change it?!

If we took this statement literally, a 300lb. male powerlifter and a 125lb. female beginner both wanting to lose fat should be on the same training program? Same exercises? Sets? Reps? The recommendations are borderline ridiculous (being nice).

In the next post we will take a closer look at EPOC and how you can maximize your effort and time with each training session.