My parents raised, trained and sold German short haired pointers and English Spaniels. There was never an overweight dog in our kennel. We fed them twice a day a vet recommended diet of dog food in the recommended amount for their weight. They never had a snack. If they didn't eat the total amount for a couple of days they got a checkup on their health, as that usually indicated a dog that wasn't well. A dog that is hungry will eat. A pet that is over fed can be particular about its diet, but it will not willingly starve. It may lose a few pounds trying to convince its owner that the food dish is not filled with its favorite food - but who is the dog and who is the boss? Dog food companies spend tremendous amounts of money getting the nutrition correct in their mix of ingredients. You get to chose according to what you want for your dog - but you shouldn't let the dog chose what it eats and how much it eats. By nature a carnivore (your dog) will eat on a feast and famine schedule, only pets never get to the famine part of the schedule - only the feast, feast, feast. An overweight dog needs to eat less and exercise more just like a human does.