Bad idea. You can use meditation for this (https://www.satanisgod.org/www.angelfire.com/empire/serpentis666/Weight_Loss.html), and generally exercising and eating healthy balanced diet with a low caloric deficit will get the job done in a healthy way.
The way to lose weight is with consistent exercise, positive affirmations and a proper diet. If you're eating fast food all the time and you're not a body builder you're going to be hurting yourself more often than not.
Not necessary, nor efficient in the long run. While it will give the spleen the "time" to remove excess weight (classified as dampness), it will also severely weaken the kidneys as they are forced to provide for the entirety of the energy of the body.
The long term implications of this come through the kidney yang being sapped through the fasting. The kidney yang powers the spleen yang, and the spleen yang is necessary to remove dampness.
A more sustainable approach to this would be to adopt a kapha-based diet, which is based around lighter foods and more veggies, which promote for the removal of dampness while still maintaining healthy energy levels. This includes lots of veggies, healthy grains, lighter meats such as fish, and less oily foods.