A 17-year-old girl is taken to her physician by worried parents. Never overweight, in the past six months she became determined to reduce from her baseline weight of 59.1 kg (130 lb). Her height is 1.7 m (5 ft 6 in.); her body-mass index (the weight in kilograms divided by the square of the height in meters) is 21. Through dieting and exercise, she lost 13.6 kg (30 lb) and stopped menstruating four months ago; her current body-mass index is 16. She denies having any problems and is annoyed that her parents, friends, and teachers are concerned. How should she be evaluated and treated