--- - |2 Abstract People are frequently dissatisfied with their body weight. Messages alleging that lower weight is esthetically preferable, healthier, and achievable likely trigger chronic self‐integrity threat, the sense that one's personal adequacy is in doubt. We examined whether self‐integrity threat, which creates stress and pressure to restore self‐integrity, contributes to the challenges of weight and behavior change. Weight‐dissatisfied women completed in‐lab tasks including a values affirmation manipulation and two‐month follow‐up. Affirmed women lost weight relative to controls, replicating previous research. Effects were primarily among those with higher initial body masses. Affirmed higher‐weighted women also ate more healthful foods compared to unhealthful foods in self‐reports and observation. Affirmed participants reported increased exercise, and an exploratory measure showed that their cortisol awakening responses synchronized with their coping needs, suggesting more adaptive physiological function. Results suggest that self‐integrity threat is an under‐recognized barrier to change, and reducing it can support healthy changes. - European Journal of Social Psychology, EarlyView.