It is usually associated with a time intervals of 12/12, 16/8, 20/4, 23/1. This means that in any of these intervals, a longer period is one when you do not eat or snack (liquids such as tea, coffee and water, are allowed), and a shorter period is when you may eat one or two times. This dietary regime is now gaining popularity not only in conjunction with keto, but also with HN. Until the energy received from food is “processed”, the body will not use its own reserves as a source. The role of such reserves in humans is performed by glycogen (it is found in the muscles and liver, and is synthesized from carbohydrates) and fat (the one we want to get rid of when we go on a diet). Essentially, the fat burning process is not triggered if digestion is taking place. Intermittent fasting involves increasing the intervals when there is no supply of energy from outside. While there is no food, the insulin hormone is not produced, this is the so-called insulin-free period. At this moment the body has the ability to switch to getting energy from its own fat. Paradoxically, an increase in physical activity will not speed up the process of losing weight, because the body is more willing to burn fats as a source of energy during moderate exercises or at rest. With intensive training, when the load exceeds 50% of the maximum threshold value, carbohydrate reserves (that is, liver and muscle glycogen) are consumed rather than fat.