Some dogs stay slim on any Burns food. Before I switched to raw feeding it was the best kibble for William, who had various skin and tummy problems plus had put weight on when on Arden Grange Light
. But Burns suited him really well. He was slim and had good skin and no tummy troubles. I know that others on here have posted in the past that their dogs lost weight and got skinny on Burns, so it's worth considering.
If you have a look on their website and contact them they're usually helpful and will send you some samples of the different varieties so you can see if Oscar likes it.