Body dissatisfaction is pervasive among young women in Western countries. Among the many forces that contribute to body dissatisfaction, the overrepresentation of thin bodies in visual media has received notable attention. In this study, we proposed that prevalence-induced concept change may be one of the cognitive mechanisms that explain how beauty standards shift. We conducted a preregistered online experiment with young women (N = 419) and found that when the prevalence of thin bodies in the environment increased, the concept of being overweight expanded to include bodies that would otherwise be judged as “normal.” Exploratory analyses revealed significant individual differences in sensitivity to this effect, in terms of women’s judgments about other bodies as well as their own. These results suggest that women’s judgments about other women’s bodies are biased by an overrepresentation of thinness and lend initial support to policies designed to increase size-inclusive representation in the media.