Why is "lean" dangerous?

Can someone give me one specific health problem, and explain it. !

Does the weight loss program have practical significance? a. no, the program is not practically significant because the results are likely to occur even if the weight loss program has no effect. b. yes, the program is practically significant because the results are too unlikely to occur by chance. c. yes, the program is practically significant because the amount of lost weight is large enough to be considered practically significant. d. no, the program is not practically significant because the amount of weight lost is trivial.

What can friends provide to affect mental health positively? a)peer pressureb)challengesc)conflictd)companionship