It would be hard to measure how the attitudes changed. In general the more people have a condition, the less having that condition makes you stand out, the less does conformity drive you to avoid that condition. Furthermore it would seem to me that "self blame is bad" is a relatively recent idea, as well as blaming everything on metabolic disorders...

Not that those don't play a role. Obviously someone with low levels of certain thyroid hormones will have to ignore hunger more than someone with high levels.

Recent research is finding that gut bacteria affect how nutrients are absorbed.

Human digestion is already very efficient... potential gains due to some different bacteria should be insignificant (and would generally be a good thing, i.e. being able to live on less food is good).

So far as rebound from dieting is concerned, you've got a point about starvation events. On the other hand, a lot of people do report gaining about twenty five pounds after each diet, so there may be something new involved.

Yeah, I dunno. There's definitely something wrong about discontinuity in response to a smoothly changing variable.

edit: an observation, traditionally we'd eat a lot of soups - e.g. borscht, etc. Those are low calorie foods that make you feel full. Now, if you go to a fast food place, or even in a restaurant, there's literally nothing which is low calorie but makes you feel full. Obviously, if you eat the volume of french fries equivalent to the volume of borscht, you're going to be over-eating. West also used to start eating with a soup.