Introduction Anti-fat attitudes reflect a type of discrimination on the basis of body weight and are one of the last accepted types of social stigma. Objective To evaluate the effect of exposure to priming messages about the causes of obesity on attitudes toward fat people. Method Participants (n = 580, M age = 22.19, 64.1% female) were randomly assigned to one of three possible conditions and then provided responses on three AFA subscales: Dislike, Fear of fat, and Willpower. Results Priming participants with messages confirming/challenging the weight controllability belief was associated with higher/lower levels on Willpower respectively compared to the control group. Unexpectedly, participants in both confirming and challenging groups showed significantly higher scores on Fear of fat. No differences were found on scores indicating Dislike. Conclusion The current findings emphasize the effect of exposure to information about the causes of obesity on weight controllability beliefs.