our jrt was a little barrel at one time, and ate just about anything. we had him on an obesity dog food from the vets, because he's a terrier he was only allowed 95g a day, which i split in to 2 meals for him, so he didn't feel left out when the others had there meals. he is now a lot slimmer and we have him on James wellbeloved senior light, and he seems to be maintaining his weight and has a new lease of life, playing with the others etc.

good luck