This study used balance theory to illuminate the relations of eating-related attitudinal consistency between self and friends to psychological well-being and eating behaviors. It was hypothesized that attitudinal inconsistency, relative to consistency, would predict lower well-being and poorer eating habits. A population-based sample of 2287 young adults participating in Project EAT-III (Eating Among Teens and Young Adults) completed measures of psychological well-being, eating behaviors, and eating-related attitudes from the standpoint of self and friends. Of participants who cared about healthy eating, those who perceived that their friends did not care about healthy eating had lower well-being and less-healthy eating behaviors (fewer fruits and vegetables and more sugary beverages per day) than those who perceived that their friends cared about healthy eating. Conversely, among participants who did not care about healthy eating, those who perceived that their friends cared about healthy eating had lower well-being and less-healthy eating behaviors (more snacks per day) than those who perceived that their friends did not care about healthy eating. In accord with balance theory, young adults who perceived inconsistent eating attitudes between themselves and their friends had lower psychological well-being and generally less-healthy eating behaviors than people who perceived consistent eating attitudes.