Vet wanted Gizmo on a lower in fat dog food as well. We tried SD Ideal Balance and he seemd to get a little of an upset belly. I asked the vet if Natural Balance LID Chicken small bites would be okay and I think it's 10% fat and 20% protein and the vet okayed it. He seems to like it. No tummy troubles.
I know looking for the low in fat is frustrating. Espeically when you walk into Petsmart and get attacked by the Blue Buffalo peeps.

Wow, I'm just bashing Petsmart this week.