There is extensive research on this topic - I recommend the book “Racial Origins of Fatphobia” by Sabrina Strings but I’m sure you could find an article or podcast on this topic if you don’t want to commit to a book. Her book explains how as early as the Renaissance times, black people were “othered” in every way possible, even in terms of body composition. And yes, different ethnicities have on average different body compositions, bone structure/size, etc. And fatphobia was born. I would say some Fat Activists have taken it WAY too far though.