What a beautiful cat!
When I put Roo on a diet it was hard for him-and me. He would always be following me around meowing "Feed me! Feed Me!". What I started doing was giving him other things in between meals. Like tuna juice, or a few kitty treats, or a little wet food. as long as he was getting something other than one meal a day his disposition was much better.
I hope that helps! He's gone down from 25 pounds to 19. (last time he was weighed)