This study tested discontinuity patterns across the stages of change. Fat intake, theory of planned behaviour (TPB) variables, and felt and potential ambivalence were assessed in 16–17 year olds (N = 187). Across the stages of change there were: (a) linear increases in TPB variables, (b) linear decreases in fat intake, and (c) quadratic relationships with felt and potential ambivalence. Although felt and potential ambivalence were moderately correlated, the correlation between the two was significantly higher in the action and maintenance stages. The findings are consistent with the idea that successful actors/maintainers are vigilant with respect to lapses.