Fasted Cardo…the what and the why
Many people love to use fasted cardio as a means of ‘stripping’ body fat and losing weight.
Fasted cardio is normally done after an overnight fast, 8-12 hours of no food intake, and then carrying out 30-60 minutes of aerobic exercise. Studies have been carried out, looking into the hot debate over the benefits of this and if it actually does help burn body fat to help people get leaner and change their aesthetic appearance.
The science seems to show that exercising whilst fasted, in a moderate aerobic setting, does indeed lead to more mobilisation of fat cells for use as energy. This appears to be down to the fact that there is little to no glycogen available to be used as a fuel source, or certainly less than normal and so fat cells are tapped into for some fuel.
So it works then right!?
Well not quite…in the studies on the aesthetic and weight loss aspect of this, there seems to be almost no difference between the fed and fasted groups who carried out the aerobic exercise. Both groups saw a drop in body fat and body weight. Almost no difference was seen between groups. There have been no other studies to my knowledge at the time of writing to contradict these findings regarding body composition.
So, it seems that, sadly, those early morning fasted runs, cycles, circuit sessions may have been in vein if it was purely for body composition!
Fasted, easy aerobic work may not be a complete waste however. It does appear that during the fasted aerobic sessions, that the predominate fuel source IS fat. So if we were involved in training for an aerobic endurance sport, or for a sport that required quick recovery between multiple events in a day (a big, strong aerobic system is needed for this) then there could be some benefits to easy training in a fasted state. The fat oxidation we see, is slowly encouraging a more ‘aerobic’ nature potentially.
There is also the benefit that for me, I often do train twice a day. If this is the case then sometimes I find it hard to eat breakfast and go straight into training, the food isn’t digested properly and detracts from my training, making me feel lethargic and often nauseous. So I regularly train fasted early in the morning, and as long as I have eaten well the night before, the sessions never seem to suffer due to this. In fact, I think the time of day and fact I am fasted actually raises cortisol levels and the fact my stomach is empty allows my body to full focus on the training and some of my best sessions have been early fasted work.
The key with this however is understanding what is happening in the body…cortisol will be left very high by this. So bringing it down quick after the training is important. So recovery protocols are important to observe strictly if you do this.
See below for the study referenced above.