What is the fast diet or 5/2 diet ?
It is a diet based on intermittent fasting , but which is done only two days a week and not on a daily basis.
On the two-day-a-week diet, you eat up to a maximum of 500 calories per day.
The rest of the days you can eat normally.

FAST DIET OR 5: 2 DIET: FEATURES

Conceived by dr. Mosley and journalist Mimi Spencer , the fast diet is a weight loss program that is based on this simple principle: if your body is used to burning a thousand and you give it a hundred for just two days a week, it will tend to burn more rather than let those hundred suffice.

This is what they call intermittent fasting, but in its simplest form. You eat normally for five days and in the two days of fasting you limit yourself to 500 calories  a day, so you do a regime that we can define as semi-fasting .  

An intermittent fasting diet that works

There are many explanations that can be given, but the fast diet works.
I am opposed to absolute fasting  without criteria, typical of those who skip meals thus thinking of losing weight and then run into the so -called compensation effect . Fasting should not be done like this, and to women in particular I recommend not the days of total fasting (24 h).
An intermittent fasting diet such as the Fast diet is therefore more reliable.