Association between anticipated follow‐up duration and treatment outcomes in anorexia nervosa: Insights from a Japanese medical prison

Abstract Aim Recovery rates in eating disorders generally improve with longer follow‐up periods. However, the effect of a longer follow‐up period itself on prognosis remains unclear due to high dropout rates. This study examined whether treatment outcomes in anorexia nervosa are influenced by the anticipated follow‐up duration, using a unique cohort from a Japanese medical prison, where follow‐up periods are predetermined by sentence length. Methods Data from 149 patients diagnosed with anorexia nervosa were analyzed. Logistic and Cox regression analyses were performed to identify predictors of favorable outcomes, defined as sufficient clinical improvement to allow transfer back to the original correctional facility. Results Longer remaining sentence length, representing an anticipated follow‐up duration, was associated with favorable outcomes ( p < 0.001), independent of the actual hospitalization duration. Higher body mass index at admission and a lifetime diagnosis of an eating disorder also predicted favorable outcomes. Factors previously associated with treatment dropout, such as low educational attainment and adverse childhood experiences, were not predictive of outcomes. Conclusion Longer remaining sentence length was associated with favorable treatment outcomes. Although this variable was conceptualized as a proxy for anticipated follow‐up duration, physicians' expectations were not directly assessed. Therefore, the findings should be interpreted as observational and hypothesis‐generating rather than causal. Future research is needed to determine whether physicians' expectations regarding anticipated follow‐up duration influence treatment processes and outcomes.