Canned food is very important to help cats lose weight. It is closer to the cat's natural diet (unlike dry food, which is mostly grain which cats are not biologically designed to metabolize), plus it has fewer calories for the same volume because of its high water content.
What some people do is give the cat a pre-measured quantity of premium dry food (maybe 1/4 cup a day), but feed it as a treat instead of as a meal out of a bowl. Do this by waiting till the cat is a little hungry and tossing the individual pieces of kibble across the room for the cat to fetch. The cat thinks he's getting a great treat and gets some exercise in the process, plus it's a way for you and your cat to spend some quality time together. Innova Evo is the best choice for dry food since it is completely grain free.
If you choose to use a lite food, then I do recommend Nutro Natural Choice Complete Care Weight Management...but I prefer seeing a cat have their diet be more of a quality canned food (or a vet approved homemade diet formula).
Increasing excercise is very important - placing food up or down a flight of stairs is one easy way, or up on a counter that you don't mind feeding your cat on
Schedule a play session daily - using an interactive toy such as wand toy to get your cat chasing and running a bit, or if your cat loves to play chase, rolling a favorite ball toy for them to chase10-15 minutes.
Another option is getting a treat-dispensing ball (yes, they make them for cats as well as dogs) and put just a few pieces of food in there, make them work for their crunchies
Okay, this might be a little too harsh for the amount your cat needs to lose, but if you need to get kitty to loose a good amount of weight in a short amount of time, but him on a French style Green Bean diet.
I swear it works even though it sounds crazy, and the cat will eat it if nothing else is available. I would also give him a few tablespoons of wet food a day as well just so he'll get some of the nutrients he needs.
Wow! If you are proposing a nothing but green beans diet, this is not safe...please, no one consider this!
Cats are not like humans, they can not be put on a rapid weight loss diet, and just pull the nutrition they need from the fat they are losing. Cats need gradual, safe, supervised (yes, I am going to tell you to co-ordinate this with your vet) weight loss.
Having just seen a rescue cat I was involved in placing die of liver failure after this very plump girl didn't eat enough during her very stressful time in a shelter/transition to new, loving home...I am very sensitive to the fact this really does happen when a cat loses weight too rapidly.
I just switched my 4 cats to Innova Light dry food a few months ago. They also split a 5.5 ounce can of food twice a day (Nutro or Pet Gold). By just switching their dry food to the "Light" I have already seen a small difference in their weights. My cats are very picky, so I wasn't sure if they would go for light food. So far, everyone likes the new food though.
What I don't like about light cat foods is reduced protein and more carbs. Cats are designed to eat protein and fat but not so many carbohydrates. I think more wet food and smaller portions of regular dry food are the way to go. If that doesn't work feed wet food only or only a very small amount of dry in addition to the wet.
When I didn't know much about high quality cat food and believed the vets knew so much about feline nutrition, turns out they don't, I fed my cats the Hill's t/d dental diet. It has only 265 calories per cup, but my cat Spotty gained weight eating it and he ate constantly like he was starving because the problem with these light foods is that they really do have to eat more to feel satisfied and when the protein is reduced, they have to eat more just to get the nutrition they need. Innova regular is a great food but their light version is only 26% protein. Iams weight control is 28% protein. Natural balance light is 27% protein. I check these things out and I don't think it's good for cats to have less than 30% protein in their diet. I think they need more than 30%. Canned food has more than 40% protein on a dry matter basis but is less concentrated and it's water content really fills them up. I hate diet cat foods with a strong passion but understand that is just my opinion.