A method to lose weight quickly , or lose fat mass without (almost) affecting the lean one? Dr. Fung, a nephrologist, has no doubts: you need to fast twice a week to lose weight quickly. A somewhat radical approach, if you will, which is the basis of his book:  The Obesity Code: Unlocking the Secrets of Weight Loss , but which according to Dr. Fung is what people have been used to for centuries. Periods of fasting (or food shortages) with successive periods of food abundance were once the practice: but since modern man has experienced a period of constant well-being, he has parallel lost the metabolic advantages of fasting. Which are: reduced fat mass, increased metabolism (during fasting). The important thing is that the fast is short, i.e. it does not exceed 48 consecutive hours, but two 24-hour fasts per week are also fine. Fung is categorical. Those who want to lose weight should refrain from eating two days a week: in this way, once the glycogen stores are exhausted, the body draws directly from fats (gluconeogenesis).

To do this, Fung recommends refraining from eating for two days in a row or for two full days a week. During the fast, you can drink green tea, coffee, cups of broth from animal bones or fish bones with herbs, a little salt and spices. Nothing else. Not even, unlike other intermittent fasting schemes such as the Warrior’s diet, centrifuged fruit and vegetables, juices or small portions of vegetables. Zero.
Of course, a bit extreme, especially taking into account the side effects of fasting in those who are not at all used to doing it, and ranging from headaches to fatigue. Additionally, people with cardiovascular health problems should refrain from such prolonged fasts

Another uncertainty concerns the moment in which you return to eat: it is true that during fasting fats are broken down (lipolysis), but it is also true that many studies have focused on what happens when you return to eat. Lipase activity is increased, so the body tries to convert food more into fat . Between the initial lipogenetic activity and that of the lipase in refeeding, the lipogenesis is however higher, and therefore in essence we should lose more fat mass than we regain. Furthermore, it seems that fasting lipogenesis does not work in the same way for obese and normal weight people, to the disadvantage of the former.
According to many people who follow Dr. Fung’s method, the method nevertheless works and would allow us to eat freely for the other five days.