Welcome to FDMB
It is overwhelming the word Feline Diabetes, but the good thing is that it is manageable, with the right insulin, home testing and the right diet, and lots of cuddles. what insulin was Fred Prescribed? ProZinc and Lantus are the best insulin for cats, they are a 12-hour insulin and easy on the cats, now if you are stating that he was prescribed 1 unit, it must be that his glucose levels are quite high, then he needs insulin, and yes a low carb diet of wet can or raw foods is a must for a diabetic cat, and the "prescription foods" ( good thinking, ) are far from being a healthy food for them they contain anything between 20-30% carbs, cats cannot digest carbs, most members here use Fancy Feast Pates between 0-10% carbs most feed up to 5% , grazing is not a good idea you need to have a feeding schedule, if you are not home during the day a wet food feeder mis a good idea, some have cameras, and several small meals/snacks 3-4 during the day, beside the two main meals before shooting insulin, the Drs approved food list has many brands to choose from, the third column will contain the carb% for each, Are you home testing? it is very important to test the glucose level before giving insulin to avoid a hypoglycemic episode, most members use the Relizon Premier human monitor and strips (Walmart) very inexpensive and accurate, no need to spend on an expensive Pet Meter. also a CGM the LIBRE if you are not home during the day is an option as well, although manual testing may be necessary with the CGM since it reads low numbers lower than reality and you want to confirm, please keep posting any concern you may have, are her for you, in our main menu we have sticky notes with much valuable information
https://catinfo.org/docs/CatFoodProteinFatCarbPhosphorusChart.pdf