Study reveals teenagers with obesity consume more calories later in the day, highlighting the role of circadian rhythms in eating behaviours

A new study conducted by researchers at Mass General Brigham and the Warren Alpert Medical School of Brown University has found that adolescents with obesity tend to consume a greater proportion of their daily caloric intake later in the day compared to their peers with a healthy weight. The research sheds light on the influence of the body’s internal biological clock, or circadian system, in shaping eating behaviours and could have implications for future interventions in weight management and metabolic health.

The findings, published in the Proceedings of the National Academy of Sciences (PNAS), add to the growing body of evidence suggesting that meal timing, in addition to calorie consumption, plays a crucial role in overall health. Researchers sought to isolate the effects of the circadian system from external factors such as social cues, light exposure, and daily routines, allowing for a clearer understanding of how biological rhythms regulate food intake.

Investigating the Link Between the Circadian System and Eating Habits

“Going into this study, we knew that the circadian system affects hunger and metabolism. What remained unclear, however, was whether the circadian system—when isolated from influences of environmental and behavioural cycles, including the light, sleep, and activity cycles—directly influences food consumption,” said Frank A.J.L. Scheer, PhD, professor of Medicine and director of the Medical Chronobiology Program at Brigham and Women’s Hospital. “This study is the first to demonstrate that food intake itself is regulated by our internal body clock.”

To investigate this, researchers conducted an experiment involving 51 adolescents aged between 12 and 18 years, with an average age of 13.7 years. Participants were divided into three groups based on their body mass index (BMI): 24 individuals with a BMI in the healthy weight range, 13 classified as overweight, and 14 as having obesity.

To ensure that external influences such as light exposure and social schedules did not interfere with results, participants were placed on a carefully controlled routine in a dimly lit environment. They followed an artificial 28-hour sleep-wake cycle, which gradually shifted their biological clocks out of sync with the natural day-night cycle. The controlled setting removed access to natural light and external time cues, ensuring that any variations in eating habits were driven primarily by internal biological rhythms rather than external environmental factors.

During the study, participants were provided with six fixed meal opportunities during their wake period. They were allowed to eat as much as they wanted from a standardised menu, while researchers meticulously recorded the quantity of food consumed and the time at which it was eaten.

Findings Reveal Distinct Eating Patterns Based on Body Weight

The results demonstrated a clear trend across all groups: calorie consumption was lowest in the morning and increased as the day progressed, peaking in the late afternoon and early evening. However, there was a significant difference in eating patterns among participants based on body weight. Adolescents in the overweight and obesity groups consumed substantially more calories later in the day compared to those with a healthy weight.

These findings suggest that biological rhythms may play a role in promoting late-day eating, particularly in individuals with higher body weight. The study raises important questions about how circadian misalignment—such as eating at biologically suboptimal times—could impact long-term metabolic health and contribute to weight gain over time.

Potential Implications for Adolescent Health and Future Interventions

Adolescence is a critical period for growth and metabolic regulation, making it essential to understand how sleep-wake cycles and circadian rhythms influence eating behaviours.

“The critical nature of adolescent development to set the stage for a lifetime of health highlights the need to understand the roles played by sleep/wake and circadian timing processes for eating behaviour,” said Mary A. Carskadon, PhD, lead investigator of the study from the Warren Alpert Medical School. “The knowledge gained here opens a door to potential interventions that can enhance teen health moving forward.”

While the study provides strong evidence of an association between circadian rhythms, eating habits, and weight status, it does not establish whether altered meal timing contributes to obesity or if pre-existing obesity influences circadian-driven eating patterns. Further research is needed to determine whether adjusting the timing of meals—such as encouraging earlier eating or aligning meals more closely with the body’s natural rhythms—could play a role in supporting weight management and metabolic health in young people.

Given the growing prevalence of obesity among adolescents, understanding the biological underpinnings of eating behaviours could pave the way for targeted strategies to improve health outcomes. Future studies will explore whether interventions that shift meal timing can mitigate the risk of obesity and related metabolic conditions, providing a potential avenue for improving long-term health in young people.