Why do you gain weight eating 700 calories a day?

yeah, i have read allot of answers about loosing weight and taking in fewer calories. I lost 90 pounds in 4 month's by eating 700 calories a day and not be active. If the these people knew anything thing about nutrition, they would have mentioned that there are 3 different body types, ektomorph,(thin people) mesomorph (the well build people) and the endomorph (the roundish people) I am an endomorph, so i tend to pick up weight no matter what, i virtually must starve my self to loose weight. I mean I have skinny friends, who eats up to 4000 calories a day and not pick up a single pound of fat, so all these clever people who tells you to exercise, don't believe them, you wont die, its about looking good and feeling good. I managed to keep the weight of, it becomes a habit.

So all these wanna bees nutritionist, please post your degrees, because you are confusing the strong will powered people who wants to change.

They want to loose weight quick, 2 months or so not 10 years.