I don't buy the teaching ones body to burn fat theory.

In practical terms, going forward it would only apply if on a regular basis you did not provide the body with carbs/sugars. As soon as you reintroduce those more easily accessible fuels the body will choose that pathway over burning fat. far better to just find a workable balance of food sources and create a long term sustainable lifestyle around their consumption.

The big problem with all these diet and exercise fads is that they are unsustainable (or not sustained) long term.