Watch the new CBSN Originals documentary, "Speaking Frankly | Fat Shaming," in the video player above. It premieres on CBSN Sunday, August 23, at 8 p.m., 11 p.m., and 2 a.m. ET. Perched on a couch, Sabrina Strings relates the story of a conversation she had with her grandmother. "My grandmother is a Black woman from the South, grew up during Jim Crow, and for her, being able to eat regularly was a triumph. One time she told me that she got a basket of oranges one Christmas and it was one of her happiest memories," she recalled. "But when she decided to move to California in 1960, as a lot of Black people were doing at the time ... she encountered for the first time a lot of White women in her integrated community who were on diets, and she was like, 'What? Why are White women on diets?' This was something that she puzzled over for years, because no one could really provide her a satisfactory answer." It was her grandmother's stories like this one that inspired Strings, who is now a sociology professor at the University of California, Irvine, to pursue research on the history of fat-phobia — the fear of fatness due to the stigmatization of weight — in the Western world. Fatness wasn't always culturally undesirable in the Western world. For centuries, being heavier was actually considered an attractive characteristic. Artists like Peter Paul Rubens and Titian famously portrayed heavier female bodies as the pinnacle of beauty in their works. As the art and fashion historian Anne Hollander wrote in a New York Times article from 1977, "The look of actual human bodies obviously changes very little through history. But the look of ideal bodies changes a great deal all the time." While the 1977 Times article considers the switch to thinness as the preferable body type to be part of "a period of revolution in both taste and politics" in the late 18th century, Strings' research traces how that "revolution" is actually rooted in slavery and Protestantism. "With the dawn of the slave trade, skin color was the original sorting mechanism to determine who was slave and who was free. But as you might imagine, with slavery progressing through the century, skin color became a less reliable source of sorting various populations," Strings explained to CBSN Originals. "Therefore, they decided to re-articulate racial categories, adding new characteristics, and one of the things that the colonists believed was that Black people were inherently more sensuous, that people love sex and they love food, and so the idea was that Black people had more venereal diseases, and that Black people were inherently obese, because they lack self-control. And of course, self-control and rationality, after the Enlightenment, were characteristics that were deemed integral to Whiteness." Strings found that these ideas about Blackness were "synergistic" with Protestant and Christian ideals. The "Protestant ethic," initially coined by sociologist Max Weber in 1904-1905, describes the concept of hard work and self-discipline as highly valued traits that would lead to eternal salvation. The "mortification of the flesh," or the act of putting sins related to the body to death by abstaining from certain pleasures, is a concept common to all Christian denominations, reflected in practices like fasting or abstinence. Strings says that many of these ideas were taken up by Anglo-Saxon Protestants in the U.S. in the 19th century. "What they wanted to do was show that they were both morally upright and racially proper, in the way in which they ate and how they maintained their figures," said Strings. "And so, they were very clear that to be of the elite race and to be a Christian peoples means that you need to show what they would call temperance in the face of food — or restraint is the way we might think of today — because if you did not show temperance, that was evidence that you were one of the savages, and also, that you were un-Christian." While the medical community and public health officials continue to study the serious health risks associated with obesity, Strings' research provides context around the social and cultural issues related to weight — and the legacy of racist and outdated ideals embedded in many of our common assumptions. "We cannot deny the fact that fat-phobia is rooted in anti-Blackness. That's simply an historical reality," she said. "Today, when people talk about it, they often claim that they don't intend to be anti-Black ... they don't intend all of these negative associations, and yet they exist already, so whenever people start trafficking in fat-phobia, they are inherently picking up on these historical forms of oppression." © 2020 CBS Interactive Inc. All Rights Reserved.