Thin through loin area

Question
I have a 9 month old intact male GSD. He eats well,gets plenty of excise and training, but to me he seems very thin through the loin area. The vet does not seemed concerned, but I would like to know when I could expect him to fill out.
Thank you for your time.

Answer
A quote from the manual  large dog guide school gives those fostering puppies for them, ''Note: German Shepherd puppies typically will look very thin throughout puppyhood.''  They mostly breed Labs, Goldens, and Shepherds.  That is the only breed specific reference in the whole manual.  Maybe he will fill out a little more in his second year.  

Shepherds are much less likely to eat themselves to a shorter life, but here is a quote from the newsletter from a different school, ''Obesity is the number one nutritional disease affecting dogs. It's estimated that 25-45% of dogs in the US are obese. Studies have shown that joint and locomotive problems increase by 57%, circulatory problems by 74%, respiratory problems by 52%, skin problems by 40% and cancer by 50% in animals that are overweight.

Large breed dogs that are overweight also are more prone to developing hip dysplasia. Obesity is especially dangerous for young puppies, as their underdeveloped frame cannot support the extra poundage that it must carry.''