Objectives. The primary objective of this study was to describe and investigate a cognitive distortion associated with eating psychopathology. This distortion, termed ‘thought-shape fusion’, is said to occur when merely thinking about eating a forbidden food increases the person's estimate of their shape or weight, elicits a perception of moral wrongdoing and makes the person feel fat.

Design. Two studies were conducted. The first was a psychometric study and the second utilized a within-participants experimental design.

Methods. In Study 1, thought-shape fusion was assessed in a sample of 119 undergraduate students using a questionnaire. In Study 2, 30 students with high thought-shape fusion scores participated in an experiment designed to elicit the distortion.

Results. Thought-shape fusion was found to be significantly associated with measures of eating disorder psychopathology. The questionnaire used to measure thought-shape fusion had high internal consistency, a good factor structure accounting for 46.2% of the variance and predictive validity. The results from Study 2 indicated that the distortion can be elicited under experimental conditions, produces negative emotional reactions and prompts the urge to engage in corrective behaviour (e.g. neutralizing / checking). This corrective behaviour promptly reduces the negative reactions.

Conclusion. The results of the two studies indicate that the concept of thought-shape fusion is coherent, unifactorial and measurable. It is associated with eating disturbance and elicits negative emotional and behavioural responses.