In exactly the same way as all fad crash diets work the bulk of the weight lost is just fluid that goes back on. Ten pounds of fat would equate to 35,000 calories so unless your intake reduces by 7,000 calories a day for the five days it would not be fat that is metabolised. Even half of this would require you to have been eating around 5,500 calories a day currently which I very much doubt you are honey.
The only benefit of the 5dpt is that if you follow it to the letter it might get your eating habits back to the basics of high protein very low carbs. Good luck with it