Don't get me wrong YW the Bulletproof Diet is definitely on the fad side of the equation. Intermittent fasting such as 5:2 and 16:8 aren't really diets per se Chasing, they're a way to ensure your calorie intake matches your expenditure. There are also marked health improvements that go along with intermittent fasting that maybe even more important than the weight loss element.
My older two boys are twiggy sticks, not an ounce of spare fat on their bodies. I think the way they eat is completely in tune with their bodies' requirements. When they're hungry they ask for food, when they're full they stop eating no matter what's left on their plates or whether it's food they really like. Occasionally they devour everything in sight for a while then abruptly grow out of all their clothes. They eat a healthy diet most of the time so I'm quite relaxed about the occasional McDonalds or other treat. The only thing I'm really against is soft drinks which they are rather too keen on IMO. My eating on the other hand has been screwed up by being forced to 'clean my plate' as a child. I just keep eating until the food is gone no matter how much there is. I can't even feel that 'full' signal any more because of having to override it for years.
I have always had a particular interest in nutrition and the research at the moment is getting vairy interesting. The Framingham Study is now on its third generation and they are adding in investigation of genetic variations. For example people that possess a copy of the ApoE4 gene seem to be genetically programmed to store saturated fat. Even if they eat a calorie-restricted diet their bodies will still convert carbohydrate to fat and store it, all while decreasing the metabolic rate to conserve as much energy as possible. So if you're an ApoE4 carrier no amount of reduced calorie dieting is going to shift the weight.