If your cat is underweight then the general guideline is not to restrict food for a diabetic cat until its weight returns to normal, with the exception of the 2 hours before each preshot blood glucose test (to make sure it's safe to give the next dose).
Not sure about how the liver and anaemia issues might complicate things.
I very much recommend that you give your vet a quick call to explain that Wenz's appetite is slow and confirm what to do about insulin dose? It's really important that a cat on Humulin N eats a fair amount before the insulin dose is given. Also, because Wenz has a history of DKA it's very, very important that he does get insulin regularly. (Note: a reduced dose is better than no insulin at all.) Perhaps your vet could prescribe an appetite stimulant for Wenz? Also, please read the following page to see whether Wenz is showing any signs of nausea when he tries to eat (very common problem in cats recovering from DKA):
Nausea and appetite problems - symptoms and treatments
Let your vet know about any nausea symptoms. Generic ondansetron and Cerenia are very good anti-nausea treatments for cats. If Wenz is suffering from nausea then these medications could help him to eat a lot better (and the appetite stimulant is better given AFTER anti-nausea med).
Mogs
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