Feeling fat reflects difficulties in processing emotions and is an important aspect of body image and eating disorders. The current study aimed to develop a novel social comparison manipulation to induce feeling fat and to explore personality traits that may increase an individual's vulnerability.At time 1, 254 healthy females (24.14 years, BMI = 23.77) completed the feeling fat subscale of the Body Attitudes Questionnaire, as well as self-report measures of alexithymia, interoceptive sensibility, physical appearance comparison and perfectionism online. At time 2, a subset of 107 participants (22.39 years, BMI = 23.85) were randomly assigned to a condition: negative social comparison, positive social comparison, negative general, or neutral (as a control).At time 1, greater tendency to feel fat was significantly associated with difficulty identifying and describing feelings (alexithymia), poorer interoceptive sensibility, higher socially-prescribed perfectionism, and greater engagement in physical appearance comparisons. At time 2, participants in the negative social comparison condition reported significantly greater increases in feeling fat compared to the control condition, but only when they were also high in alexithymia or socially-prescribed perfectionism.Current findings provide new insights into the potential mechanisms underpinning feeling fat and highlight how a novel social comparison manipulation can be used to induce the sensation of feeling fat.