This is something I struggle with too.

I have eight cats - the eldest three are 15, 14, 14, and are all overweight. My vet has said not to worry too much about getting them to diet as they are very healthy for their ages, but I obviously don't want them putting any more on.

I then have two other cats who are just over two who are both slightly underweight and three who are 14 months who are just right.

At one point I was trying to feed senior food, adult food and kitten food - but gave up! My cats all go outside, I work quite long hours but do pop home a couple of times most days, so they get food down throughout the day. If the two who are underweight are in I will put them in another room and feed them but they spend more time scratching at the door to get out than they do eating!

Some eat dry, some eat wet and some will eat both. I feed raw occasionally and the youngest three will eat it but not the older ones.

My eldest three are quite lazy and sleep on my bed a lot so I am trying to encourage them to exercise more as they will still play if I dangle a toy mouse in front of them. I think increasing their exercise is easier than trying to get them to eat just 'light' food.

Good luck with your fur babies.