when he was diagnosed on January 22nd he weighed 17 pounds, now he weighs 15 pounds. The vet wants him at 12-13lbs based on his size.
Sounds like a very similar story, to George, he was too fluffy, just short of 9kg(19llb) at diagnosis he had lost weight and body condition/muscle tone he was down below 7.5kg. (16llb) (still overweight), his weight crept up a bit once he got regulated and then I watched his calorie intake so that gradually (very slow) he is down at 6.5-7kg(14-15llb) his ALT was also raised at diagnosis, but was normal when we did the BW again.
I used the calorie counter in that link and it says my cat should be consuming about 318 calories a day based on his ideal weight
that's to maintain weight, but if you want him at 12-13llb he still needs to loose, a bit so when I put the figures in it comes out at 240. FWIW when I've used that calculation, George put weight on, it seemed to overestimate it for him.
Have you had a look at DR lisas site
Catinfo.org.
This is from her section on feline obesity.
Hepatic lipidosis can also develop when a cat consumes 50% or less of his daily caloric requirements over a period of many days. The definition of “many” varies from cat-to-cat. For this reason it is important to understand that you need to have some idea of the calories from canned food combined with the calories from dry food that your cat is consuming on a daily basis while you are implementing the transition to canned food.
I have never seen a cat develop hepatic lipidosis when consuming at least 15 calories per pound per day. This number is figured on lean body weight, not fat weight.
If your cat weighs 18 pounds but really should weigh 12 pounds, please make sure that he is consuming ~180 calories per day. (12 pounds lean body mass X 15 calories/pound/day = ~180 calories/day)
In practice I aimed for somewhere in between the calculator and the above calculation.
I have a yoga class to get to, so I have to dash out, I will get back to you later on, there's some other links I am just struggling to find at the minute.