That won't happen because it never happened in the first place. The people of the middle ages were like us -- they broadly liked slender people, women with perky breasts, and men with broad shoulders.
This should not be surprising. Attraction is pretty hard-wired into humans by evolution, and for most of our existence, food has been scarce. There is absolutely no reason why a time of more plentiful food due to agriculture (relative to most of human history) would have resulted in changing the body types we generally prefer. To say nothing of evolution's timescales, which are measured in tens of thousands of generations for significant changes like that.
The post has a ton of links, and r/askhistorians is one of the most heavily vetted and moderated subreddits in existence. I'm sorry it's not what you wanted to hear, but no, fat people were not attractive in the middle ages because of food scarcity. Because there was no food scarcity. Relative to human history at the time, there was an abundance of food.
This should not be surprising. Attraction is pretty hard-wired into humans by evolution, and for most of our existence, food has been scarce. There is absolutely no reason why a time of more plentiful food due to agriculture (relative to most of human history) would have resulted in changing the body types we generally prefer. To say nothing of evolution's timescales, which are measured in tens of thousands of generations for significant changes like that.
https://www.reddit.com/r/AskHistorians/comments/8044k7/is_it...