In the FatLand National Museum, there is an exhibit entitled "Fat and Fear." There is another exhibit entitled "Fat?" It is the second one I'm thinking about now. The question it poses is "Who is considered fat, and why?"
The ironic part of this is that even during the Pro-Health and Diet reign of anti-fat terror, not all admins and staff even agreed about who was fat, and who wasn't. Technically people were supposed to be considered overweight if their BMI was above 30, and overweight if it was above 25. Yet they ran into a problem very quickly. Can you guess? Some people who had BMI's of x looked fatter than those who had BMI's of x+5 or even x+7. The admins learned, to their chagrin and embarrassment, that it was very difficult to tell exactly what someone's BMI was just by looking at her or him.
They also learned later that they also could not figure out what someone's eating habits were just by knowing her or his BMI. People they scorned as fatties could be vegans. People they considered slim and trim could be scarfing down two gigantic steaks or burgers per day.
And even more embarrassing to the admins who were sincerely concerned about maintaining the health of the citizens of their nation: they couldn't tell even from someone's "health habits" (eating and exercise patterns) how healthy he or she was. People who ate very little sugar developed diabetes. People who had never smoked developed lung cancer. People who ate sugar every day did not develop diabetes.
A couple of admins all but admitted that the classification of "fat" was proving to be problematic. And a study done in FatLand simply reconfirmed that the most important indicator for anyone's weight was genetic, and that setpoint weights was not very malleable. It also reconfirmed that every person has/had a unique nutritional blueprint, and that although this does change in some ways during his or her life, most of the foods which provide the most nutrients to anyone are those he or she likes most - unless, of course, this blueprint is affected by starvation or yo-yo dieting, which can set off eating disorders, including but not limited to bulimia, anorexia and binging.
What does all this have to do with who is and is not considered fat? It turned out that the people most likely to be called "fat" and sent to Reeducation Centers (aka Fat prisons) were those who were not following the diet and exercise plans prescribed by the Health and Diet Admins, even if their BMI's were the same as or even a bit less than those who were following the prescribed plans. Of course all of them were harassed by both staff and anti-fat bigots, but if someone could show that he or she was following the plan and was being monitored daily by an admin, that person probably would not be sent to a Reeducation Center. A "bad" fatty, one who was not following the "plan," would be sent, and would be labeled "fat" much more readily.
Even these days, on the OtherSide/USA, someone who is wearing fashionable, costly clothes and accessories to match, someone who is concealing most of her flesh, and smiling -believe it or not, the "smiling" part is an important part of this- and is not seen eating in public, is less likely to be called "fat," even if she is the same size as someone else who is eating an ice cream cone, wearing clothes that are not fashionable, or are baggy, or tight, or someone who is fat and showing -gasp!- more flesh than the bigot thinks is "nice."
So if we stop to consider, "fat" is often more of a political term than anything else and connotes someone who is not controllable by the constraints of fashion and by anti-fat bigots.