Instead of gaining the freshman 15 my son lost. Should I be worried?

Not, unless to thin! Most people gain the weight because of less physical activity. And eaitng too much bad food. If your son is playing a sports, either varsity, or intramural, he may be burning off calories from actrivity. Many colleges have gyms better than private spas. And the answer most likely to please mom; your home cooked meals are better! anyway, with an obesity epidemic, unless too thin, don't worry!