800 calories are very little whether you are a little or very overweight. There is no problem in having a very low-calorie intake for a period of time. Since there is everything you need of essential nutrients in Nupo, including vitamins, minerals, fiber, and proteins, there is no health risk in a very low-calorie intake for up to 8 weeks. After 8 weeks, take a break for 1-2 weeks with energy-reduced food, after which a new course of up to 8 weeks with Nupo diet can be started.
If, on the other hand, you should eat plain food and only consume 800 calories, you would not be covered with vitamins and minerals. With regular food, you need a minimum of 1200 calories to be covered in regards to nutrition.