When it comes to pumpkins and helping your cat lose weight, there is some truth to it. However, while some aspects make them an ideal option for weight loss, some things make them not as good compared to other methods.
Pumpkins are ideal as tasty, high-fiber foods that also provide a relatively small amount of calories.
This can result in you and your cat enjoying a pumpkin's taste while also feeling fuller for a longer period of time while also not gaining too many calories. Thus battling obesity.
HOWEVER, just as pumpkins are low in calories, they are also largely irrelevant for most cats outside of the fiber. This means your cat would be filling their stomachs up on nothing from a nutritional standpoint.
Instead, it's recommended to feed your cat low-carb wet canned food or to work with your local vet for a specific and personalized weight loss plan for your cat.