The diet works like any other version of the intermittent fasting diet. It helps reduce the number of total calories you are consuming.
It is very difficult to determine the number of calories you would normally eat in a week when you only have five days. If you start fasting for 24 hours twice a week, you will find it a little difficult to overeat as your stomach will shrink even after you fast.
When you extend the fasting period, your body has to use the stored glycogen from carbohydrates and fat for fuel. When the body uses the stored glucose and glycogen, it switches to a ketogenic state and burns fat for fuel. That is why it is better to fast longer when it comes to weight loss.