Having access to more space to move around in should help in time. I've always had cats and have had a few that were overweight for short periods of time, but usually around the age of twelve or thirteen, when their activity levels are down. When they get to be in their twenties, the problem reverses and you have to try to keep weight on them. I live in a small town, and I have a back yard, so my cats are able to go outdoors during the day, so that helps. When I have lived in places where they could not go outdoors, I did have to make time to play with them from time to time throughout the day, a favorite toy being Da Bird, which doesn't require a whole lot of work on my part, but cats love it.
I have not often had to limit the amount of food available for my cats though, and I have two that are twenty-six right now. I free-feed them kibble which, perhaps because it's always there, is not something that they feel the need to gorge. Then I split a can of food between the three cats twice a day.
One possible problem might be the food. Cats are made to eat primarily meat. Given a choice, cats don't eat things like corn, soy or wheat, and many cats don't digest it well. Yet, these are common ingredients in the less expensive brands of cat food. Because it doesn't contain much of the meat that they need, they eat a lot of it, much of which turns into fat, while a lot of the stuff their bodies can't use ends up in the litter box. Look for something that has meat as its main ingredient, including chicken, turkey, or other fowl. Cats digest fish well too but, given the problems with nuclear waste in the oceans these days, I worry that the fish used in pet foods may have high levels of stuff that isn't good for them. I do still feed them foods with fish, but not as much as I used to.
Look at the ingredients of whatever you're feeding them, and eliminate anything that uses corn, soy, wheat, gluten or by-products. By themselves, there's nothing so terribly wrong with by-products because cats in the wild wouldn't reject by-products, but the types of by-products that go into pet food is too often some pretty nasty stuff. In kibble, you will find some ingredients that cats wouldn't ordinarily eat, such as rice, potatoes or a variety of vegetables. Some of these ingredients are necessary in order to form the kibble, and do have some nutrient value. Brown rice is better than white rice, but rice shouldn't be the first ingredient. The first ingredient should always be meat, fish or fowl.
To a point, you get what you pay for. The best foods for your cat are probably going to cost more, but there are some fairly expensive foods that are nevertheless expensive, which is why it's important to read the ingredients. If you are on a budget and you have a Tractor Supply Company store near you, they have a line of premium foods at prices that will rival the cheap stuff, called 4Health. I use Blue Buffalo kibble because my cats like it and have done very well with it, but the ingredient list in the 4Health kibble and canned food is very good, and I do include the 4Health canned food in their rotation.
Switching from a grocery store brand food to a premium cat food has never been a problem for any of the cats that I have had, but it is often recommended to mix the new stuff with the old stuff for a couple of weeks to let them get used to the new stuff. When a cat is used to having to eat a lot of a food in order to get its minimum requirements of nutrition, they might continue to eat the same amount of food after you've switched them to a premium brand, and sometimes even more if they enjoy the taste.
Usually, this is temporary though. Within a few weeks or a month, their bodies will adjust, and they will realize that they don't have to eat so much. At that point, some people will wrongly assume that their cat doesn't like the new food because it's not eating as much of it, when the truth is that the cat's body realizes that it doesn't have to eat so much volume in order to get the necessary nutrition. The fact that most cats will eat less of a premium food than of a less nutritious food offsets the added cost of the premium food.
However, cats are individuals. Not every cat can be safely free-fed. I did have to quit free-feeding for a while, after taking in a cat that couldn't walk past the kibble without eating. I know that feeling, except for me it's refrigerators. The reason for a cat being overweight are usually pretty much the same as the reasons for a person being overweight. Either they are eating too much, eating the wrong things, or they aren't exercising enough, or a combination of these.
