First off I am no vet but I would not recommend extra calories just to get extra calories. You don't want bad weight that can lead to a plethora of other nasty problems like urination blockage ( dependant on the food ) as well as diabetes.
I'll relate a story of mine. Around 3 years ago my cat began to lose a ton of weight due to diabetes. Bony but with a massive pouch. I was determined not only to get him back into shape but also to get him off insulin. I searched around did tons of research to find the highest proteins available. I don't care what anyone says, cats are carnivores, and cats are felines. The amount of similarities they share to even Lion and Tigers far exceeds any human qualities. Many foods take diets that work for people and translate it into cat food. Bad idea. When's the last time you saw a wild feline that wasn't built for destruction?
I switched to 100% wet canned food. He got dry stuff during the day but only because I wanted food available while I was at work. Cats do not eat Breakfast, lunch dinner. They dont need to be fed twice a day. In fact, cats will often "graze" numerous times throughout the day. So I pretty much gave him all of the highest protein wet food that he wanted ( be sure to check that the Meat ingredient is one of the first three and ACTUAL meat, not a "meal" or "by-product".
My result? A 14 year old cat, no belly pouch, and built better than he ever was at any age. Almost went into remission for diabetes as well.
It may take a while to get things down, but you could try a good real-meat-ingredient, wet-canned food diet. Pay attention to how much is consumed per sitting. When you find out, just keep on filling the dish with that amount whenever you see it empty. Keep in mind though that some cats may get bonier due to age and that is just how things are. Be patient too. What I accomplished above probably took about 6 months.
Last edited by marie73; 04-07-2018 at 07:11 PM.