[tripzilch]

Stored fat in a teenager going through a growth spurt??

Their bodies (and brains) are doing a lot more developing than just growth spurting, which is why such a teenager can eat huge portions[0] per day and not put on any fat at all. Because their bodies use it all up, because of all the transformations and puberty things going on.

I would suggest, in that stage, just giving the body everything it craves, and worry about the benefits of fasting later.

[0] obviously doesn't hold in parts of the world where these are considered "normal" portions.