"You should really be watching your weight," she said, which created a momentary vision in my mind of being asked to watch a friend's luggage at the airport while she darts to the bathroom to take a pee, but I know that's not what she meant.
"Watch your weight" is code for "get less fat."
The thing is, I know that the science behind "fat=unhealthy" is bad. I've read numerous studies on the subject and I've written about it. I could have countered her on purely medical grounds with discussions about set points and health as a complex issue, and how fat hatred and the diet industry drive mainstream medical approaches to weight. And I could have said, too, that people have a right to be treated like human beings regardless as to their weight and health risks.