This is such a difficult question to answer, though a very reasonable one to ask. Every dog is different and every owner has their own way of thinking about things.
The correct amount of food to give to your dog is the amount which produces the correct bodyweight. That is a simple statement, but medically is true. So ideally you would offer an amount of food, weigh your dog periodically, then increase or decrease the amount so that you produce and maintain a dog of perfect weight. The trouble with that is that in most situations, the correct amount is a small fraction of what your dog would choose to eat, and probably a small fraction of what you feel you need to give. Probably many dogs would feel genuinely, desperately hungry on the correct amount of food, would be pestering permanently for more, and you would feel sorry for him and give more, so he will remain fat.
Everyone wants a diet that is enjoyable to eat, fully satisfies hunger, and produces the perfect bodyweight. Sadly it is like the Yorkshire farmer who first saw a giraffe, then proclaimed "there ain't no such animal!" Many dogs will either feel hungry all the time, or it will be fat. (In fact often both!) If you had only ever given him very boring, tasteless food, it might be that he would nver have got fat. Now he knows what it is like to enjoy eating a good meal, he will always want to do so. Boring food does not appeal, nor does remaining feeling hungry.
If an overweight dog was given to me, he would lose weight and he would end up a nice slim dog, happily bouncing around and enjoying himself. He might well also always be on the scrounge for food, but I would ignore that and leave him hungry, unless he was getting too thin. I would make an honest assessment of the sort of amount of food he had been getting, then I would provide about half that quantity in a good quality dried food. I would get a container which held what I judged to be the correct amount, fill it up at the beginning of the day, then feed two meals a day plus the occasional treat, all from that one container, measured out every morning. After 2 weeks I would weigh him. If he had lost a suitable amount, I would probably stick to the same diet. If he had lost more than that I might increase the amount of food slightly. If he had lost less weight, I would feed less from then on. Then I would weigh him and continue like that every 2 weeks. I would end up with a healthy, slim dog, but I know he would always be hungry. That is all there is to it.
I have talked to a huge number of owners of fat dogs. Some of them end up with nice slim dogs, most cannot bring themselves to feed to the "correct" amount of food. The deciding factor is the feeder, not the dog or the diet. It is all down to the person doing the feeding. Apart from that, it is really very simple.
Sunday 20th January 2013