Need Help for Overweight Cat

Help!
My 4 year old cat is gaining too much weight. My problem is that I have a 12 year old cat who is underweight. I've switched to light cat food and I do not have food sitting out all day for her but I have to make sure that my older cat is getting enough food. Does anyone have any proven way to help their cats lose weight?
Any suggestions would be appreciated. Thanks! Pat

If you don't leave food out all day, is it a possibility to feed them in separate rooms?

Light food in general does not help overweighr cats but won't help your underweight cat gain any weight either.

There is information on how I helped my obese cat lose weight here

Have you tried extra feedings for the older cat? Does she appear to be hungry?

I can sympathize. I have three cats - Carly (who is known as daddy's little football because of her shape), Much (who is 13 and is very thin) and Lucy (who is a little heavy and very darn picky).

We have Wellness Healthy Weight out all day. They don't really like it but it is there when Much gets hungry. Carly gets wet food twice a day. Lucy gets her special Purina UR twice a day. This is the only food she will eat and it is for her badder stone. We have to watch that Carly doesn't eat the UR so we spend a lot of time picking up and putting the food back down. We used to have this out all of the time, but that is when Carly was packing on the ounces. Much, the skinny one, gets a couple of wet meals in the evening. We will also give her several wet meals during the day when we are home. We have to watch that Carly doesn't disturb Much. I think if she was more intrusive we would put her into another room. Fortunately, when we tell her no, she obeys.

So far, Much has held steady and Carly has lost 6 ounces. But it is an adventure making sure everyone eats the proper food. Hubby calls it herding cats time.

I've found it takes a lot of discussions with your vet and experimentation for what the cats will tolerate. Good luck.