There's a lot of scientific evidence supporting a ketogenic lifestyle, distinguishing this movement from fad diets and Attia from a Guru status. If you're interested I would recommend the following book: http://amzn.com/0983490708
He suggested I try working out while fasting. Just don't eat 3-4 hours before working out, and have a high quality protein 'meal' (I drink a shake) after the workout.
So far it's been working for me. And I've been working out since I was a young teenager- some three dozen years now.