This largely depends on the breed of dog, diet and age. If it is a young dog (less than 7) and is a normally active breed, look at diet. If the diet is a general manufacturer, then it's possible there is some diabetes, or other internal issue. Take a look at the AKC website for your animal's breed under characteristics. Go to a PetsMart or similar store and read up from more than one source. If it's that important, I'd even take the animal to the vet and get some lab tests run. Most of all, get the vet involved! Having raised and trained German Shepherd Dogs, the vet is my first stop, not an internet chat or Q/A room.