Abstract
BACKGROUND: In Japan, approximately 20-25% of young women are underweight, highlighting a significant social issue with considerable future health risks. This generation is strongly influenced by the internalization of thin ideals, leading to a belief that being thin equates to beauty and a misconception that it equates to health. Recent studies have revealed that young women with insufficient physical activity and low dietary intake exhibit metabolic profiles similar to those of obese individuals, putting them at increased risk for developing diabetes in the future. Addressing these issues requires a multifaceted approach, with stable exercise habits crucial for enhancing body satisfaction by reducing the internalization of thin ideals and improving self-esteem. Given this context, it is essential to investigate the effects of exercise habits, particularly in underweight women. Therefore, this study investigates how exercise habits influence body satisfaction by mediating thin-ideal internalization and self-esteem, comparing these effects between underweight and normal-range weight women. METHODS: The study surveyed 400 young women aged 18-29 who are underweight and 189 with normal-range weight across Japan, assessing their exercise habits based on the Ministry of Health, Labour and Welfare's National Health and Nutrition Survey criteria (exercising at least twice a week for over a year, with sessions lasting ≥ 30 min), subjective body satisfaction, sociocultural attitudes toward appearance, and self-esteem. Data analysis was conducted using the PROCESS macro for SPSS, which allowed for mediation analyses to test indirect effects. Thin-ideal internalization and self-esteem were analyzed as mediators of the relationship between exercise habits and body satisfaction. Mediation analyses were performed separately for underweight and normal-range weight groups to identify differences in the mechanisms underlying these relationships. RESULTS: Approximately 50% of participants in both groups reported regular exercise (average 2.5 days/week). In the underweight group, exercise habits fully mediated the relationship between reduced thin-ideal internalization, increased self-esteem, and improved body satisfaction. In the normal-range weight group, exercise habits reduced thin-ideal internalization and improved body satisfaction but had no significant effect on self-esteem. CONCLUSIONS: The results highlight that the pathways through which exercise habits affect body satisfaction differ according to body mass index. For underweight women, reducing thin-ideal internalization and enhancing self-esteem through exercise habits is crucial. In contrast, interventions directly boosting self-esteem may be more effective for women with normal-range weight. These findings clarify the distinct roles of exercise habits in influencing body satisfaction for underweight and normal-range weight women in Japan.