According to an online study, humans can live up to 2 to 3 months without food (if drinking water). Logically, if you can go months with 0 calories, you can certainly go 24 hours at 800. However, people with certain health conditions may be unable to restrict calories in this way. The extended pack has modifications for higher calories that you can use to adjust this die face. Always consult with a healthcare professional before beginning any new food plan.