How do you differentiate between positive and negative fitness goals?

Most of the girls in my friend group are obsessed with fitness. They will be the first ones to tell you that it is really an obsession. One of them asked us to reschedule our weekly lab meetings so she could go to a specific fitness class during the day (rescheduling would have required canceling other work obligations). Often, we will go out for happy hour and no one will actually eat or drink anything other than diet coke.

Another girl recently embarked on a fitness program that has put her 1 pound away from being underweight (133 pounds at 5’11” and 15% body fat). Her trainer said, “Let’s see how low you can go.” She complained that she was getting migraines that strangely coincided with her workouts, but insisted they were unrelated. Now she is singing the praises of her trainer to anyone who will listen.

Some of these people have struggled with eating disorders in the past. They all insist they are making healthy choices now.

They look like (and some are) models. They say they feel great. Am I just being judgmental in thinking they’ve all gone overboard? When are diet and exercise choices positive and healthy, and when have they gone too far?