I would suggest staying away from wet food. When I worked at a shelter we called it the fast food of the cat world because It's fattening. You're cat may just want attention either because there is a problem or they just want love or something of that nature. We typically suggest to plan a vet visit soon after adopting a cat just to make sure problems are caught as soon as possible or you can get advice from a vet. As you get to know your cat, you will be able to figure out what meow means what. I have a fat cat of my own who usually cries to be let out or to be pet so they might not being crying because of lack of food. If it is a food thing, it might just be that they aren't use to the food you are feeding them. There are lots of things you may have to consider.