It seems simple though to assume that our brains protective nature gets called into play due to a lack of consistency. Yes we do overeat from time to time, but we also under-eat. As I've said time and time again, persistence and consistence is key to weight-loss. Treat your body right, teach it that food is abundant and you won't have a problem. Switch from under-eating to overeating and your simply telling your brain that it no longer has to survive in very uncertain times.
When it comes to nutrition, quantity is equally important as quality. Just make sure your figures add up!