How it works: All exercise builds muscle and burns fat but your body can only build muscle when it has the materials (protein) and the energy (carbs) to do so. Meal #2 is precisely that - the materials and the energy required. Your body will only burn fat when there is no energy left available from your previous meal, that's the only time it'll turn to your body's secondary fuel tank - fat cells. 16 hr fast acts as a safeguard, it ensures that once your body has used up everything it needed for recovery and muscle fiber re-building it doesn't put anything in reserves (your fat cells). You continue using the energy you got from the meal #2 (what's left of it) and once it's all gone your body turns to your fat reserves until meal #1. Then the cycle begins again.
You want to time your meals so you burn fat during the day (working, thinking, breathing) and then build muscle after a training session with the aid of Meal #2.