Why is weight such a big deal?

Well this morning there was a note in my mailbox at school saying they needed me to bring my first period class to the health office. They needed to record the height and weight of the students. Now I have a class with all all girls and 2 boys. They are all juniors and seniors in HS and like many young( and middle aged etc) women they are very concerned about the stupid number on the scale. Now the girls in my class are beyond pretty and not one of them have a weight problem, but I know the anxiety that ensues when one is about to get on a scale. I told them that I felt bad because they did not know and could not prepare( ie: where the lightest outfit possible and save their 16oz of cofee until after the weight in). It is funny how even 17 and 18 year old girls understand this. The boys were not too bothered, they just saw it as a minor inconvience not an event that causes the arousal of ones autonmoic nervous system. The sad part is, I wish I could tell the girls that there would be a day that they would never think about that number on the scale, but that day probably will not come. I am still waiting for that day, I am probably more neurotic than the 17 and 18 year olds in the class. Why are we so obsessed with weight? Why cant women take a lesson from their male counterparts? I doubt we will ever be able to answer that question. I hope my daughter does not obsess, but she likely will, because all girls whether that number is too high or too low have their own reasons for not liking it.