Cut back on the amount of food you are giving him, some of the meat might have more fat than you realise - although it's hard to say if he's overweight without seeing him.
I had a "Tubbalarde" (at least that's the breed I used to call him - just say it out loud teehee). I could have sworn he wasn't a big eater, he always seemed to just pick food. That was when I was lazy and put down communal food bowls for the gang. He got bigger and bigger and bigger.....I thought he had a thyroid problem, then due to having a gobbleguts come and stay with me I had to start feeding individually - turns out my "Tubbalarde" was INHALING the food. Over a year I've reduced his weight by about a third (yes I know, naughty naughty mummy for letting him get like that). Now he just looks oh so sexy!