my cat cody and food habbits

Question
Hi, my cat cody is over a year old he had a hard time when he was younger, in
a out of the vets to which we later found that his blader had not formed to its
full size and he kept blocking it, and well lets just say it was horrible thing to
see your kitten to go through so he had a major operation. After the
operation he went back to normal for about 10 months but just recently he
has been really funny with his food, one day he we love what you have given
him the the next day you will give him the same brand of food and he will
turn his nose up at it even though secounds ago he was meowing his head off  
for the food the trouble is I leave it down for him to eat later but his sister
bets him to it, she is getting fat and he is getting very skinny and i dont know
how to fatten him up. If you put him in front of the food he will have a bit
then wonder off if you put him in front of it again he will do the same i hope
you can help and i hope that this makes sence.

Cheers Manda

Answer
Well try separating his food from the sisters, like put him in a bathroom or something.  Try feeding him his cat food soaked in tuna juice.  Or mix a little bit of can food with his solid food.  Both ways can fatten him up.  I'm not exactly sure what you were asking but I figure it was how to fatten him up.  No one can know why he won't eat the food unless he is sick. It is inside his own mind.  If you can't get him to gain weight take him to a vet asap.