Discovery Health Channel Research and Reviews Site

What is the best weight control dog food on the market?

I adopted a 42 lb. Cocker from the shelter I volunteer at in February and she's now up to 49 lbs. My vet said she's put on a lot of muscle due to the excercise program we have her on, but she needs to drop some fat off. I've tried lots of Diet foods, all-protein foods, etc. and none have helped. I follow the quanity suggestions to a tee and am getting frustrated. I've spoken to a few vets and they only seem to recommend the food they sell at their clinic!!! She's almost 9 and being this heavy is really hard on her...any recommendations?
I haven't tried the Senior formulas yet...that's something to look into.
There is nothing wrong with her thyroid. When she came into the shelter her teeth were rotting (during her first week with me she sneezed and 2 flew out) and she wouldn't touch regular dog food. I think the person that owned her only fed her table scraps and this is how she got into the shape she's in!
When I switch her food I do it gradualy, mixing the two until the mixture is all the new food.