You want to lose weight. You start trying to find the BEST way to lose fat. You come across this phenomenon called ‘fasted cardio’. It's a bodybuilders (that douche in the picture above...) favourite form of cardio.
The idea was that the body had been fasting all night while you slept; reducing blood sugar levels, decreasing muscle glycogen stores and further decreasing insulin levels. Thus if you hit the cardio before your first meal the body would have no choice but to use fat as its primary fuel source. Ever since, countless bodybuilders, athletes, and regular gym goers have been looking to cut weight; they have been clawing their way, tired and hungry, through high intensity cardio in the hopes of shedding a little weight.
Could this really be the best way to burn fat? Doing fasted cardio sounds miserable.
Some of the leanest athletes are cyclists. And what is their preferred fuel source? Carbs! So we have bodybuilders performing fasted cardio and we have cyclists cramming as many carbs as possible. Yet both are extremely lean. What's the truth? How does the body best get rid of fat?
The body is constantly adjusting its use of fat or carbohydrate depending upon a variety of factors. Generally if you burn more carbohydrates during your workout you will burn more fat post workout. While research does show that fasted cardio can increase the mobilisation of fat from the adipose tissue, this only occurs at very low levels of intensity. If a bodybuilder performs high intensity interval training (HIIT), they may see an increase in fat mobilisation but that does not mean an increase in fat oxidation. This results in all those fatty acids being re-packaged and stored back into the adipose tissue. After all that suffering you put it right back where it came from!
In general, fasted cardio at approximately 50% of your maximum heart rate has no benefit over non fasted cardio, unless the exercise last over 90 minutes... Only then did the fasted cardio begin to show favourable results. So what are we left with? The body will burn more fat cells when fasted at a lower intensity, but the volume has to be longer than 90 minutes. Anything shorter and it's no different to having some food in your belly.
So long story short: eat before you exercise! Why? Because without the fuel to fuel your muscles, you can't reach the intensity levels required to burn fat effectively. I know countless gym goers that will preach, “You got to eat before you lift bro! You need to fuel those muscles.” Then why doesn't the same principle apply to high intensity cardio? You need to fuel the muscles to perform at a high level in order to induce growth. In this case, increase mitochondrial growth and fat burning potential.
Need more reasons not to do fasted cardio? Okay!
Muscle tissue is made up mostly of protein which, in turn, is made up of amino acids. Normally, your body does not use protein to produce energy. If you run out of glycogen stores and no glucose is available, however, your body will then break down its own muscle tissue to release amino acids. These amino acids are sent to your liver, where they are converted to glucose in a process called gluconeogenesis. When your body starts to use muscle tissue for energy, you lose muscle mass. Starving without any glycogen left in the muscles to fuel their cardio efforts, folk will still hit the treadmill in the hopes of shedding more fat. What's really going to happen is your body is now going to use the protein in that hard earned muscle to fuel your HIIT session.
Think about endurance runners! Why are they so skinny? They burn so many calories during their runs that they cannot eat enough to restore glycogen stores. What happens? The body starts eating the muscle. A bodybuilder is doing the same thing to a lesser degree during the cutting phase. The question becomes, why not have some food (preferably carbs) pre-cardio, to be able to hit the intensity requirements needed to save that precious muscle mass? You will be a constant fat burning machine and not have to sacrifice any muscle mass!
You don’t need to suffer to lose weight!