I have a shepherd and experienced the same thing before. I found changing his food and exercising him more did the trick.
I changed him to 1 can of Merrick/day. Half in the morning along with 1 cup of Innova dry food. The other 1/2 for supper with the 1 cup of Innova again.
While he'll always accept any other treats and such, he no longer has the panicked HAVE TO EAT, EAT, EAT thing going on. I think some of it was boredom.