how old is your cat anyway?
have you ever visit vet? vaccine? deworming?
Are you feeding wet food all the time?
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im not sure if it is adult or kitten, kitten will always be faster eater, but if your kitten is slow eater, you need a vet.
if u never visit vet before, now it's time to wake up. vaccine your cat and deworm them. check the health status on why they don't eat that much.
wet food won't give your cat much nutrition. Get your cat a good quality dry food, such as royal canin, science plan, iams, orijen, etc. If your cat has weight problem, then you can choose kitten food, since kitten dry food contain a lil bit higher nutrition.
lastly, check your cat weight and age. if he/she is on average weight which is a good weight while eating less, then there's nothing to worry about. Unless your cat is under weight then you need a wake up call to do something. ask vet for advice.
but if vet say your cat is average weight, but you still want him/her to be fat, remember, fat always lead to sickness.
so think about, do you want yourself to be happy having fat fat cat, or having a happy cat with solid body. cat by nature born to have a solid body like cat in the wild.
My mother in law always believe that giving wet food to cats give the cats more nutrition. I always object and argue her on this. When i bought dry food for the cats (usually i bought RC or Iams) I ask her to give the cats, but at last she always give the cat nasi and mixed with fish or sometime add some fish skeleton.
I'm afraid that the cats will loose weight, FYI my cats are mix breed; i have persian, local and siamese. I'm afraid the persian would have problems in the future. They can eat nasi or not? Hehe...