I agree with the suggestions so far to try to get your cat to eat and that eating is very important. I also completely agree that home-testing blood sugar is also important.
Three other things that occur to me are:
1. Are you testing your cat (what's his name) for ketones? Ketones are a not-common side effect of unregulated or under-regulated diabetes. Untreated ketones can lead to diabeteic ketoacidosis, which can become very bad pretty quickly. Low amounts of ketones may be treatable at home; high levels of ketones may require hospitalisation in a 24-hour care facility. Because of the ability to become serious so quickly, and because of the different levels of care involved in treating them, I encourage all newly diagnosed diabetic cats to be checked daily for ketones. (You can read more on ketones here
http://petdiabetes.wikia.com/wiki/Ketones )
To check for ketones, stop by the diabetes section of your local pharmacy or grocery store and pick up a product called ketostix. I think it's about $15 for 90 sticks? You expose the stick to fresh urine and, if ketones are present, the stick changes colour. If ketones aren't present, you breathe a sigh of relief and congratulate your cat

There are various tricks you can use to get a fresh urine sample; if you have difficulty, just come back and start a new thread labelled something like 'need tips for getting urine sample'.
2. My second thought is pancreatitis, which can occur in diabetic cats with more frequency than in non-diabetic cats. From the symptoms you describe, it doesn't sound like your cat has pancreatitis, but you're also not mentioning much of anything beyond the loss of appetite so it's difficult to tell. You may want to read up on pancreatitis here
http://petdiabetes.wikia.com/wiki/Pancreatitis and here
http://www.felinediabetes.com/phorum5/r ... msg-876722 ). One of the symptoms of pancreatitis is nausea, which can be treated by giving your cat small amounts of Zantac or Pepcid A/C (*not* Pepcid Complete).
As I said, from the brief description you've given, it doesn't *sound* as if your cat has pancreatitis, but we can't be certain. But if he does, or if he has nausea or some other digestive problem, then either Zantac or Pepcid A/C may be beneficial. Please talk with your vet about whether you should try this approach.
3. Eliminating the obvious. In this particular case, your cat is recently diabetic. Diabetes can be triggered by poor oral health. And now your cat is having problems eating. So: has a thorough dental exam been done to check for dental issues, such as dental caries, or broken or missing teeth?