New research has found that the eating behaviors of teens with obesity — an “under-researched” population — are strongly influenced by their internal body clock. They also tend to eat more later in the day than their healthy-weight peers. 

Investigators from Mass General Brigham and the Warren Alpert Medical School of Brown University, US, led the study.

“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 behavioral cycles, including the light, sleep, and activity cycles — directly influences food consumption,” says Frank Scheer, Ph.D., a 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.”

Results of the study are published in the Proceedings of the National Academy of Sciences.

Setting the internal clock

The circadian system is composed of trillions of biological “clocks” present in virtually all organs, tissues, and cells, which prepare the body’s biology and behavior to the changing demands across the day-to-night cycle.

Previous research on circadian nutrition investigated the importance of meal timing in reducing fatigue while maintaining muscle endurance and cognitive function.

The influence of the circadian system is known to differ between people due to a combination of genetic, behavioral, and environmental factors.

In the Brown University study, 51 male and female adolescents between the ages of 12 and 18 (mean age of 13.7 years) participated. Teens were divided into three groups based on body mass index (BMI).

Twenty-four were in the healthy weight group, 13 in the overweight group, and 14 in the obesity group. All participants lived on seven 28-hour sleep and wake cycles, staying in a controlled dim light setting while awake and in complete darkness during sleep.

Participants stayed in the same space throughout the study. To control for outside influences on circadian rhythm, researchers removed all external time cues from the lab’s environment, including clocks and access to outside light.

With a standardized menu, participants received six opportunities to eat at fixed times across the wake episode. Participants could consume as much food during each meal as they would like. Researchers tracked food eaten and caloric intake.

During the day, teens could participate in various activities, including crafts, watching movies (with screen lights dimmed), and playing social games.

Results of the study

The results showed that changes in the circadian system throughout the day and night significantly influenced food consumption across all participants.

Food intake peaked in the late afternoon and early evening in all three groups. It was lowest in the morning, even after accounting for behavioral and environmental factors, demonstrating that the body’s biological clock directly impacts how much participants eat at different times.

While this study demonstrated the impact of the circadian system on food intake and revealed differences between groups based on weight, the researchers posit it cannot test the “chicken and egg” question of which comes first.

Future studies are needed to determine whether affecting the circadian control of food intake contributes to weight changes and if weight changes impact the circadian control of food intake, or a combination of the two.

With future research, Scheer aims to better understand the interactions between diet, the circadian system, metabolism, the biological mechanisms underlying these relationships, and the implications for developing timed dietary interventions to improve health.

“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 behavior,” says the study’s lead investigator, Mary Carskadon, Ph.D., of the Warren Alpert Medical School.

“The knowledge gained here opens a door to potential interventions that can enhance teen health moving forward.”

Other circadian diet research from the University of Waterloo, Canada, and the UK University of Oxford has developed a mathematical model to understand the resilience of the circadian “master clock” or suprachiasmatic nucleus in the brain.