A dog doesn't have to eat every day. In fact, many serious raw-feeders deliberately fast their dogs once a week and there's good reason. Understand that while our pooches are domesticated pets, their digestive systems are the same as wild canines. Think about it; wolves don't catch prey daily, but when they do, they feast like there's no tomorrow. Then they will typically fast until their next kill which allows their digestive system to take a break. Sometimes these fasts last for days.
Digestion also depletes the body of energy. That's why body-builders eat many small meals a day, they burn off energy this way which allows them to maintain an ideal weight. When a dog or even a person fasts, it gives the body a recess from digesting and lets their system relax, repair and build up more enzymes.
But there are other benefits for a fast. If your dog's stomach is a little queasy, a food-break will help to settle it. Fasting is also a natural way to detoxify the body.
So if your dog doesn't feel like eating one day, or turns his nose at the tasty dish you served him - relax. It's just nature's way of fixing a little irregularity.