Will i lose weight if i do this?

Hi everyone, this summer i am hoping to lose weight... In least 20 pounds. I've heard about a lot of diets but i am curious about this one. Basically this diet you can only eat fruits, vegetables and water. You do it for 7 days with exercise. I am not only gonna do this diet/plan this summer but i heard it will get rid of some toxics in your body? I am wondering if i would lose weight if i did exercise and that diet..?