The Impact of Circadian Rhythms and Behavioral Cycles on Caloric Intake in Adolescents Varies by Weight Status

Academic Background

The prevalence of obesity continues to rise globally, particularly among adolescents, increasing the risk of various chronic diseases such as type 2 diabetes, hypertension, and cardiovascular disorders. While previous studies have linked late eating with an increased risk of obesity, it remains unclear whether the endogenous circadian system independently influences caloric intake and whether this influence varies based on weight status. To address this gap, researchers designed an experiment aimed at disentangling the separate effects of the endogenous circadian timing system from the sleep/wake and fasting/eating cycles on caloric intake. The core focus of this study was to explore whether patterns of caloric intake differ under the influence of the endogenous circadian rhythm and behavioral cycles across adolescents of varying weight statuses.

Source of the Paper

The study was conducted by a team of researchers from multiple institutions, including Mary A. Carskadon from Brown University, Chantelle N. Hart from Temple University, Hollie A. Raynor from the University of Tennessee, and Frank A. J. L. Scheer from Brigham and Women’s Hospital, among others. The paper was published on February 18, 2025, in PNAS (Proceedings of the National Academy of Sciences), titled “Independent effects of the human circadian system and sleep/eating cycles on caloric intake in adolescents vary by weight status.”

Research Procedure

Study Participants and Grouping

The study recruited 51 adolescents aged 12 to 17 years (24 with healthy weight, 13 overweight, and 14 obese) and categorized them into three groups based on body mass index (BMI) percentiles: Healthy Weight (HW), Overweight (OW), and Obese (O). All participants were free from sleep, medical, or psychological disorders and had not traveled across more than two time zones in the two months prior to the study.

Experimental Design

The study employed a Forced Desynchrony (FD) protocol to separate the influences of the endogenous circadian system from behavioral and environmental cycles. After completing a 14-day stabilization period at home with a fixed sleep schedule (21:30 to 7:30), participants entered the laboratory for an 11-day study. In the lab, they followed seven 28-hour sleep/wake cycles, with 17.5 hours allocated for wakefulness and 10.5 hours for sleep. During waking hours, lighting was maintained at a dim level of 6.58 lux to avoid suppressing melatonin production.

Measurement of Caloric Intake

Participants consumed six meals at regular intervals during their waking period. Before each meal, participants selected food items from a fixed menu, and the research team weighed and recorded the intake. The difference between pre- and post-meal weights was used to calculate caloric intake per meal. Additionally, participants completed questionnaires assessing pre-meal hunger and post-meal satisfaction.

Circadian Phase Determination

Salivary melatonin levels were measured to determine each participant’s endogenous circadian phase. Saliva samples were collected every 20 to 45 minutes during waking hours and analyzed via radioimmunoassay to measure melatonin concentrations. This data was then used to calculate each participant’s circadian period and phase.

Key Findings

Influence of the Endogenous Circadian System on Caloric Intake

Results indicated that caloric intake was significantly influenced by the endogenous circadian system in all participants. Caloric intake reached its nadir during the circadian morning and peaked in the late afternoon. Specifically, the peak caloric intake occurred at approximately 17:30, slightly earlier than the reported peak in hunger and appetite in adults (around 19:50).

Differences Based on Weight Status

Adolescents who were overweight or obese consumed more calories later in the circadian cycle compared to those with healthy weight. Furthermore, the amplitude of their circadian rhythm (the difference between peak and trough caloric intake) was significantly lower, suggesting a weaker regulatory effect of the circadian system on caloric intake in these groups.

Influence of the Behavioral Cycle on Caloric Intake

Caloric intake decreased progressively across the waking period for all participants, with the highest intake occurring at the first meal and the lowest at the last. However, adolescents with obesity showed a more uniform distribution of caloric intake throughout the waking day, consuming fewer calories at the first meal and more at the final meal compared to other groups.

Conclusions

This study provides the first direct evidence that the endogenous circadian system independently influences caloric intake in adolescents, and this effect varies by weight status. Adolescents who are overweight or obese tend to consume more calories later in the circadian cycle and exhibit a weaker circadian regulation of caloric intake. These findings offer new insights into the physiological mechanisms underlying obesity and provide a scientific basis for future intervention strategies.

Highlights of the Study

1. Innovative Experimental Design: The use of the Forced Desynchrony protocol successfully separated the effects of the endogenous circadian system from behavioral cycles on caloric intake.
2. Weight Status Differences: The study revealed unique characteristics in circadian regulation of caloric intake among overweight and obese adolescents.
3. Practical Applications: The findings provide crucial guidance for developing personalized dietary interventions targeting obese adolescents.

Additional Valuable Information

The study also found that pre-meal hunger and post-meal satisfaction were influenced by circadian rhythms, with these effects being more pronounced in overweight and obese adolescents. Furthermore, the research team developed a detailed nutritional database to ensure accurate measurement of caloric intake.

Through this study, we not only deepen our understanding of the relationship between circadian rhythms and caloric intake but also pave the way for future research on obesity interventions.