I just read your previous post. 4 years old seems awfully young for a diabetes diagnosis. Are there any other issues with him? Infections, dental problems, allergies? Was he on steroids for anything?
It looks like you were feeding him IAMS Proactive Health Cat Food, Indoor Weight and Hairball Care. Are you still feeding him this? I highly recommend checking out the
food list as well as further nutritional information at
catinfo.org and consider switching Nom Nom to a better, low carb (less than 5-10%), wet food. The food switch alone should significantly help reduce his insulin dependency, perhaps even making him diet-controlled (i.e. needing
no insulin).
ETA: You had asked about protein options and I completely failed to address that

(and it was the main point of this second post ohmygod_smile ). I use the catinfo.org food list, but I also created
my own specialized version of it because I have two growing kittens in need of higher protein and Michelangelo is also allergic to red meats. I sorted it by Carbs, then Protein/Fat %, then Phos/100kcals, then Brand and Flavor. Various
studies have found the target range for
healthy adult cats to be around "26 g day protein, 9 g day fat and 8 g day carbohydrate, yielding a macronutrient energy composition of 52% protein, 36% fat and 12% carbohydrate." For diabetics of course, the carb percent is much lower (less than 10%).
In addition to the food, as a diabetic, Nom Nom is going to be
particularly ravenous starting out. I suggest giving a read-through of the thread on
FEED KITTY AS MUCH AS THEY WANT? for some ideas on feeding schedules and caloric intake.