I recently posted a goofy April Fool's thread about my cat's weight loss attempt. Although it was all in fun, I really did turn her health around with diet.
She was eating a really high quality dry food, and would not touch anything else. I had to practically starve her into eating other food, even wet cat food, and real meat. Dry food, even good quality stuff, is quite low in real meat.
She's lost weight, her coat is amazing, her eyes are bright, her energy is a million times higher, her cyst on her head disappeared. No supps. Just a combo of a high quality wet food, minimal dry food, and real meat (raw and cooked beef, chicken, fish) and egg whites (cooked) on a regular basis. She's ten and looks two - before she looked older then her age. It's been the most dramatic change I've ever witnessed.