Dynamic associations among selected healthy dietary behaviors, physical activity, emotion, and fitness performance in adolescents: a four-wave random intercept cross-lagged panel study.

Introduction: Adolescent diet, physical activity, emotion, and fitness performance may develop together, yet they are often studied separately. This study examined within-person longitudinal associations among selected healthy dietary behaviors, physical activity, emotion, and fitness performance across one academic year. Methods: Data came from a school-based four-wave longitudinal assessment conducted in March, June, September, and December 2025. The analytic sample included 2,209 junior secondary school adolescents with complete data across all waves (1,166 boys, 52.8%; 1,043 girls, 47.2%). Selected healthy dietary behaviors were assessed using four dietary indicators. Physical activity was measured using seven scored sections of the Physical Activity Questionnaire for Adolescents. Emotion was assessed using three emotional state items, and fitness performance using standardized endurance, standing long jump, and grip strength indicators. Random intercept cross-lagged panel models separated stable between-person differences from within-person changes. Sex-related patterns were examined using sex-stratified models and formal multigroup tests. Results: The final fully constrained model showed good fit. At the between-person level, random intercept correlations among the four domains were not statistically significant in the complete-case model. At the within-person level, selected healthy dietary behaviors and physical activity showed reciprocal temporal associations, as did physical activity and emotion. Fitness performance was associated with subsequent physical activity, whereas selected healthy dietary behaviors, physical activity, and emotion were not directly associated with subsequent fitness performance. Formal multigroup tests detected no statistically significant sex differences in the main cross-lagged paths. Discussion: Selected healthy dietary behaviors and physical activity were temporally coupled within adolescents. Physical activity may represent a potential behavioral connector linking selected healthy dietary behaviors with emotional state and functional physical capacity. Because mediation, indirect effects, and causal pathways were not tested, these findings should be interpreted as hypothesis-generating temporal associations rather than demonstrated mechanisms. The findings support integrated adolescent health promotion addressing diet and physical activity while considering emotional experience and fitness-related support.