eating disorder loosing weight

I brought home another cat and since then my other cat 13 years old has went from being plump to being skin and bones and acts like hes starving,but he eats alot.He never really ate alot of people food,but now will eat almost anything and acts like he cant get enough and runs when he thinks you drop food or call him.We leave a full bowl of his favorite hard food down all day for him and fresh water.He eats and sometimes he vomits his food up and sounds like hes trying to throw up a hairball but never does just vomits.He meows a lot when going to the bathroom.Can anybody help me out.

Answer by Kate
Hi
Please take your cat to the vet as soon as possible. It sounds to me like he either has Diabetes or a thyroid problem (it may be something else but the symptoms are in line with either of these conditions)

My own cat had a thyroid issue. She ate like a horse and got thinner and thinner. When we took her to the vet they said that she was losing so much weight that Muscle was now being eaten away and that was why she was getting weaker and weaker. She is fine now by the way after treatment.

I hope your cat is better soon

best wishes KAte