Chrononutrition Behaviors and BMI Change During the Transition to University Life in Young Adults: A Prospective Study

Background: The transition to university life is characterized by substantial changes in eating behaviors, sleep–wake organization, and lifestyle patterns. Chrononutrition-related behaviors, including meal timing and caloric distribution across the day, may influence metabolic health independently of dietary quantity, yet prospective evidence in university students remains limited. This study aimed to evaluate BMI trajectories during the first academic year and to identify chrononutrition-related behaviors associated with BMI change and clinically significant weight gain in young adults. Methods: This prospective observational study included 921 university students aged 18–24 years. BMI was assessed at university entry and after one academic year, and BMI change (Diff_BMI) was calculated. Chrononutrition-related variables included meal frequency, identity of the main meal, breakfast habits, and late eating. Multivariable linear and logistic regression models were used to evaluate independent associations between chrononutrition-related behaviors, BMI change, and clinically significant weight gain (Diff_BMI > +1 kg/m2). Results: Mean Diff_BMI was −0.45 ± 1.07 kg/m2 (95% CI −0.52 to −0.38; p < 0.001). Overall, 48.2% of participants showed BMI reduction, 38.7% remained weight-stable, and 13.1% experienced BMI increases; clinically significant weight gain occurred in 7.2% of the cohort. In multivariable analysis, having dinner as the main meal (vs. lunch) was independently associated with greater BMI gain (β = +0.22 kg/m2; p = 0.004). Male sex was associated with lower BMI gain and lower odds of clinically significant weight increase. Breakfast skipping showed an inverse association with BMI change, whereas meal frequency and late eating were not independently associated with BMI trajectory after adjustment. Conclusions: The temporal distribution of caloric intake, particularly late eating patterns and shifting the principal meal toward later hours of the day, appears more strongly associated with BMI trajectory during the transition to university life than meal frequency alone. These findings support the relevance of chrononutrition-oriented strategies targeting meal timing and circadian eating behaviors in university students.