Our dog had that same problem. The vet said "boy shes skinny" but she ate so much it was unbelievable. well first we found out she had worms (she was 6weeks old) so we got rid of thoes and started feeding her Iams. I know that GSD have a different digestave system then other dogs so they cant eat a lot of things without throwing up or in our dogs case having dirrea. So anything like sience diet (if you can afford it) or iams is awesome. and make sure not to give them any people food. ONLY the dog food you buy them. we give ours a peanut once in awhile or a small piece of cheese when she starts having that problem. Our vet also said to try peptobismol about a tablespoon to help with that problem as well. but make sure you check with your personal vet for your dog to make sure thats ok for your pet.