GSDs aren't meant to be large dogs. Females should fall between 48 and 70 lbs as full grown adults and should be between 21 1/2 and 23 1/2 inches at the top of the shoulders. This girl is in my guy's pedigree:
http://www.pedigreedatabase.com/germ...-buckower-feld
See. She's barely even up to the guys knees and skiiiiiiiiiiiiiny. This dog is in ideal physical condition. GSDs are also a slow to mature breed, they are often skinny minis until 3 years. It takes them a long time to fully fill out.
Americans are really used to seeing fat dogs
Also GSDs have notoriously sensitive digestive systems. Very very common in the breed.