Prior research suggests that knowledge calibration (KC) supports consumers’ maintenance of a healthy diet. However, no previous studies have considered that learned helpless consumers may refrain from using their knowledge, even though they may be fully aware that they possess it. This research gap is considered in three studies. Study 1 investigates the moderating effect of learned helplessness (LH) by means of a cross-sectional survey. Studies 2 and 3 are online choice studies. Besides from replicating Study 1, Studies 2 and 3 eliminate potential social desirability bias by objectively measuring respondents’ dietary choice quality. In addition, Study 3 takes into account the possibility that respondents’ responses may be biased by food preferences, medical conditions, and/or food allergies. Moreover, Studies 2 and 3 both investigate the consequences of the findings on consumers who live under a dieting regime. These studies demonstrate that consumers suffering from LH do not stand to gain from calibrating their dietary knowledge to the same degree as other consumers. It is also shown that dieting behavior has a tendency to weaken this negative moderating effect of LH on the relationship between KC and dietary choice quality. Finally, the implications of the findings for marketers and public policymakers are discussed.