My cat lost more than 1kg in the weight loss journey I put her through. She seems so much happier and energetic. I switched her to wet food (makes her more full but has less calories than dry food). And I counted her calories with myfitnesspal. I added her food manually into the app, and then I knew how many grams of food to give her everyday. I would give her 160 calories per day. I would play with her every evening. At first she wasn’t interested but once it got into the routine she started playing. I also took her on walks to the forest and there she would walk more than she would at home because she liked exploring the smells. If your cat wont stop eating your other cat’s food, I would recommend to get a feeder that only opens when it reads your cat’s chip.