What is the best way to lose weight quickly in 100 days? I would be religiously doing the water therapy. Water therapy helps you to perspire, and perspiration is one of the top ways to lose weight. Also, through this kind of treatment, you’ll be able to cleanse your body; I mean, you’ll basically have no toxic chemicals in your body for a whole 100 days. You can get accustomed to that therapy for the rest of your life.