Trying to understand about the Ideal Protein diet?

I'm a 17 year old girl 5'5 and 140 pounds. I have a pretty athletic build (swam year round for about 11 years.) Now I'm wanting to lose about 20-25 pounds and I'm having trouble with my eating plan. I know of several girls that have done Ideal Protein and look amazing and have kept the weight off. I do 4-5 hard work out sessions a week and I'm just wanting to know how much weight I would lose per week because it says you lose 3-7 just by doing the meal plan. I understand about ketosis and how your body becomes dehydrated the first few weeks if you don't drink enough water, I just want a better understanding on how this diet system works, and how it is better than others.