I'm a female and i want to know how can i gain weight?

Kind? Fat,H20,Muscle: From lots of evidence, staying slender, as long as living within environments without recurrent famines, is healthy. The more common problem in western societies, esp. The us, last few decades, is obesity with assoc. Diabetes mellitus, ↑ed cv ds rates, esp. As people get older, high bp, etc. How about being grateful for not having, and promoting oneself into these problems? Did i miss something?