Researchers have found that when very overweight people, who tend to have relatively low metabolic rates, lose weight primarily through dieting, their metabolisms generally remain unchanged  They will thus burn significantly fewer calories at the new weight than do people whose weight is normally at that level
Relatively few very overweight people who have dieted down to a new weight tend to continue to consume substantially fewer calories than do people whose normal weight is at that level.
 Such newly thin persons will, ttherefore, ultimately regain weight until their body size again matches their metabolic rate