Time-of-day effects on eating behaviors: Examining circadian timing and caloric intake patterns

Chronotype describes differences in the timing of daily rhythms, regulated by the circadian system. These patterns are classified as morning or evening chronotypes. Studies show increased impulsivity, poorer health behaviors, and greater cardiometabolic risk among evening chronotypes. However, few studies evaluate these effects relative to circadian biomarkers. Additionally, time of day may impact how chronotype affects behaviors. Participants completed an eating in the absence of hunger task during morning and evening sessions. Participants were served oatmeal, then given access to snack foods. Calories consumed from each snack type was the primary outcome. Participants fasted for ≥8 h before a 9 AM morning task. For the evening task, participants fasted for 2 h and completed an 8 PM task. Dim light melatonin onset (DLMO) was measured the day following the morning task. Covariate-adjusted models evaluated differences in caloric intake across food types and sessions, and tested associations between caloric intake and DLMO. 113 participants completed the protocol (57 female; age: M = 35.6, SD = 9.87). Significant time-of-day effects were observed, with lower intake of bland (B = -5.67, p < 0.001) and salty foods (B = -15.53, p = 0.015) in the evening. Order effects showed greater intake during the second administration for total calories and all categories (ps < 0.01). Later DLMO was linked to greater appetite ratings. These finding suggest that those with later circadian timing may have greater hedonic interest in food. Future research should explore interactions between chronotype, circadian timing, and environmental factors shaping eating behaviors.