I have a couple of old responses about standards of beauty that may help you understand this:

Ancient Greek and Roman sculptures depicted women as soft with curves. Which period of time did we begin to see the ideal female body as having a lower body fat?

Did heavier men and women used to be considered more attractive before industrialization? Are there representations of this in art or literature of the time period?

But even they're sort of incomplete, because there's so much subjective about the issue that it's hard to give a real answer. What is "fat" as a body type/size? By some standards, a woman whose upper arm squishes when it hangs at her side is too big, while by others, that's normal and unremarkable. There have been a number of periods in Western history when a thinner body has been seen as most aesthetically pleasing, but very few where the most extreme thinness was; likewise, there have been periods where a body with more flesh on its bones was seen as appealingly healthy, but none that I am aware of where the more weight = the more attractive. People have often failed to make conscious declarations about what looks attractive doing so because it signifies wealth, and trying to read past minds on the subject tends to lead to reductive, oversimplified statements.

Not Yet. There are cultures in present times where obesity is considered a mark of high social status.

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I assume that the twenty year rule applies to future events as well.