What causes rapid weight gain in females?

[tanyajack]

"The amount of lean muscle mass we have is the primary determinant of metabolic rate. In other words, the more muscle mass we have, the more calories we will burn. Our muscle mass naturally begins to decline around age 30, and that process, called sarcopenia, accelerates around age 40.

 

http://www.jrhealthblog.com/weight-gain-with-age-diet/