My Doctor asked me if my wife and I were overweight when we met as he said it is a very big concern with one partner losing weight and leaving the other. I told him we were both thin but he advised that I need to address that should it come up. Something to keep in mind though.
But as dfav said it will take some time to get him adjusted but I'd not try and involve him so much if he is pushing back as you describe.
- Aaron