That's brilliant news! I felt the same with Layla, I hadn;t realised how bad it was and then after she'd been on the diet things were so much better and she was so much mroe lively.
Something that has really helped has been the introduction of a water fountain, I have a drinkwell but there are a few on the market. The incxreased fluid intake makes the world of difference and cats definately seem to drink more when they have a fountain.