From my own personal experience, I find that fatty meat (even lean ground beef) if hard to dose for. A cheeseburger is a great example. Using 80/20 lean beef you are looking at 0 carbs for the meat (yay!) however you have 22g of fat and 19g of protein to account for. Your body is going to convert that into energy (hopefully). Add in a slice of cheese 7g of fat and 5g of protein and the bun which if you're using good old hamburger buns are 33g of carb per serving.
On paper, you have 33g of carbs! Hooray, so one small dose of insulin and you're done!
Incorrect. You need to worry about the carbs from that bun in the short term (think hour, 2 hours after eating). However that protein and fat from the meat and cheese are slow burners on the glycemic index. You are going to have to account for those over the next 4 or 5 hours.
I find that I can't treat 1g of fat/protein like carbs, but usually on have to take a bolus of roughly half the total amount of those 2 hours after eating.