Re: Science Diet Light for senior cat?
If your cat is otherwise healthy and doesn't require a special diet, I would just switch him (VERY SLOWLY) over to a good quality canned food. Science Diet is full of grains, carbs and fillers and your kitty will never lose weight on it. Also, I would stay clear of any "diet" "in door formula" or "lite" foods as well as they tend to have too many fillers as well.
Some good foods are Wellness, Innova, Evo, Merrick, Prairie, or Solid Gold.
I've got to say though, if your kitty is 17 and healthy, I don't think I would be that concerned about his weight at this point. Obviously, it's not good for them to be overweight in general, but if he's done well this far, why mess with it? But that's just me. If you really want him to lose some weight though, I would do it extremely slowly.