Even though this is more a strength orientated website, most athletes still do some form of cardio and, lets face it, most of us want to look good. So fat loss is a topic worth covering.
For ages, people have gotten up at ungodly hours and performed cardio on an empty stomach since the body then has no other choice but to burn fat. It sounds great, but is it true? Aside from the fact, that I do not think cardio is necessary to get lean (there, I said it), lets have a closer look at cardio in a fastened state.
In short, no. For the long answer read on.

While it is true that the body will use mainly fatty acids as an energy source when performing any exercise on an empty stomach, this doesn’t necessarily mean that you will lose more body fat. How so?
In the end, it is the overall calories that are being burned that matter. So while someone who does cardio in the am might use up more fatty acids than someone who does cardio in the pm, they still burn the same amount of calories. Now, if we assume a caloric deficit they will both lose weight.
I personally have several issues with doing cardio in a fasted state. First off, there is a drop in performance so the overall amount of calories being burned is lower than if the athlete had consumed some food beforehand.
Secondly, there is muscle loss. Foods (glycogen and amino acid) are anti-catabolic, hence they help prevent muscle loss during exercise. If muscle is lost, that means your metabolism will slow down, hence you will have to diet stricter to achieve the same results. now to me, muscle loss is one of the worst things that can happen. As a natural athlete, you are bound to lose some muscle during a diet as is (if everything goes well , you will lose 1 lbs of muscle for every 3 lbs of fat), but you shouldn’t try to create a situation where you are endangering your precious muscle tissue.

If you feel you should separate from cardio from weight training, at least have some BCAAs beforehand to avoid catabolism. Otherwise, do it after you hit the weights, your glycogen stores will be then be empty and fatty acids are used for energy.
‘Til next time
Maik