My cats eating habits

Question
Hi Dr.
My cat is approx. 9-13 years old (we found him) and is a very picky eater to the point that I worry because he never has put on weight (he is about 7.5lbs) and is bony.  Over the past 4 years we have tried everything from kibbles to cans and even homemade food but to no avail.  He usually likes a new food for about 1 week and then turns his nose up at it.  He has bad teeth so I worry that some food may be painful for him to eat.  Do you have any suggestions to encourage him to eat?
Thank You
Kate

Answer
The bad teeth can lead to infection in the kidneys and liver.  Best bet is to have a chemistry screen and CBC blood tests done to check for underlying organ disease and then get his teeth cleaned and any bad ones extracted....he should also be on some antibiotics.  I would also try feeding canned food versus dry.  Try Natural Balance as cats find that very appealing and it is all natural.