While I haven't done Insanity yet, I have done P90X and am starting Turbo Fire again right now. The best thing I did was buy a heart rate monitor. I just put it on before whatever workout I do so I know exactly how many calories I have burned. Sometimes I use the calories if I'm really hungry and sometimes I don't. I think what is even more important than the amount of calories is the types of calories your eating. During these workouts you need to make sure you're fueling yourself with the good stuff and just listen to your body's signals. I know I've had days were I ate all my calories but was still starving and sluggish because I chose empty calories over the ones full of the nutrients my body needed.