We use a combination of Humalog and NPH in 4 to 6 injections a day. As a general rule, he needs about.75 units of Humalog per exchange of carbohydrates. Injecting with a meal works great because the action of the Humalog coincides with the release of glucose into the bloodstream from the carbohydrates.
Fats are another matter entirely.
Oftentimes, he has a peak 2 to 3 hours after a meal, long after the Humalog has done its duty. Obviously, we don't count the fat grams when we calculate a meal-time injection because he would just crash. But we frequently have to give a second shot about 3 hours after a high fat meal to bring his blood sugar into acceptable range. We avoid fatty foods as much as possible. But, hey, he's a kid first, and sometimes that means pizza.