Not a result of insulin but instead the disease itself. It'll cause constipation due to dehydration. Remember how your kitty was drinking water like crazy and peeing like crazy? His body is trying to force out all that sugar and taking all that liquid with it. Once you stabilize him with insulin his peeing will go back to normal and his constipation will subside. Try giving him some cat grass to loosen his stool. Others feed pumpkin mixed in with their food. Hopefully you're feeding him a low carb wet food now and got away from dry food, dry food will make his constipation that much worse. Wet food will soften his stool and lower his carb intake. Pate style wet foods are the best, those like Fancy Feast or Friskies.
