A friend of mine has obviously brought her metabolism into starvation mode by performing strict low-calorie diets (without any exercise) for over ten years. This has resulted in a yo-yo effect where she can hardly eat more calories than her basal metabolic rate without gaining weight, so she diets again every few weeks.

What is the best way to break this vicious circle of dieting and gaining weight again after eating normally? How can she bring her metabolism out of starvation mode?