Well, if it worked last time why do you have to do it again?
A diet is a quick-fix option for weight loss not fat loss which puts your body under a lot of stress it is simply not used to.
If your body is under stress, it releases something called cortisol which it uses for energy. But this only occurs by breaking down muscle tissue. And if you burn muscle tissue, your body will go into defence mode and start storing fat for protection.
This is the point when you start to feel low in energy and weak.
Muscle weighs more than fat, so if you lose muscle tissue you are losing weight but gaining fat.
Then, when you start to eat normally again (which is guaranteed to happen), your fat percentage will be higher than when you started due to the body protecting itself. Then you start to gain muscle leaving you heavier than before.
This leaves you in the 'rebound effect' assuming it worked last time. However, these diet companies thrive off you failing as you come back again and again, so business booms!
You should be following a sensible food plan day-to-day in order to help you drop healthy body fat combined with a good training program to help improve muscle mass.
Make sure you eat something from every food group and leave nothing out. Get rid of sugars, limit takeaways to a treat when you earn them and look at the produces you are consuming.
My advice is, if it's living, grows in the ground or on a tree eat as much of it as you want.
To keep it simple, that's meat, fish, fruit and veg!
For the month of February I am offering 50% off nutritional consultations. This will provide you with a one hour, one-on-one session to discuss the ins and outs and you will take away your own food plan.