A study on adolescents uncovered a crucial link between circadian rhythms and eating habits, showing that teens with obesity tend to consume more calories later in the day.

Conducted in a controlled environment, the research confirmed that internal biological clocks directly impact food intake, independent of sleep and light cycles. Scientists aim to explore whether shifting meal timing could help manage weight.

The Link Between Obesity, Circadian Rhythms, and Eating Habits

By 2030, nearly half of Americans are projected to have obesity, a condition that increases the risk of chronic diseases such as diabetes and cancer. While past research has linked sleep, eating habits, and weight gain, the exact role of the circadian system — our internal biological clock — in shaping eating behaviors has remained unclear.

A new study from Mass General Brigham and the Warren Alpert Medical School of Brown University sheds light on this connection, particularly in teenagers — a group whose eating patterns can have long-term health consequences. The study found that adolescents with overweight or obesity consumed more calories later in the day compared to those with a healthy weight. These findings suggest that circadian rhythms play a key role in regulating food intake, especially in individuals at risk for obesity. The results were published in the Proceedings of the National Academy of Sciences (PNAS).

Internal Body Clock and Food Consumption

“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,” said Frank A.J.L. Scheer, PhD, a professor of Medicine and director of the Medical Chronobiology Program at Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system. “This study is the first to demonstrate that food intake itself is regulated by our internal body clock.”

Adolescents in the obesity and overweight groups consumed significantly more calories in the circadian evening compared to those in the healthy weight group. Researchers found no significant differences in total sleep time between or within the groups across sleep cycles.

How Circadian Rhythms Shape Eating Patterns

The circadian system is composed of trillions of clocks present in virtually all organs, tissues, and cells, which prepare our biology and behavior to the changing demands across the day/night cycle. The influence of the circadian system is known to differ between people, due to a combination of genetic, behavioral, and environmental factors. This study uniquely highlights the correlation between weight class, calories consumed, and circadian rhythms in adolescents, an under-researched population whose current eating patterns will play a crucial role in shaping their long-term health as adults.

Fifty-one male and female adolescents between the ages of 12 and 18 (mean age of 13.7 years) participated in this study. 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.

Participants received six opportunities to eat at fixed times across the wake episode, with a standardized menu. 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 a variety of activities including crafts, watching movies (with screen lights dimmed), and playing social games.

The Biological Clock’s Direct Impact on Eating

The results showed that changes in the circadian system throughout the day and night significantly influenced food consumption across all participants. In all three groups, food intake peaked in the late afternoon and early evening and was lowest in the morning, even after accounting for behavioral and environmental factors, demonstrating that the body’s biological clock directly impacts how much we eat at different times of the day.

While this study demonstrated the impact of the circadian system on food intake and revealed differences between groups based on weight, it cannot test the “chicken and egg” question of which comes first. Future studies are needed to determine whether affecting circadian control of food intake contributes to weight changes, if weight changes impact the circadian control of food intake, or a combination of the two. With future research, Scheer aims to gain a deeper understanding of the interactions between diet, the circadian system, and metabolism, the biological mechanisms underlying these relationships, and the implications for developing timed dietary interventions to improve health.

Potential for Health Interventions

“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,” said the study’s lead investigator Mary A. Carskadon, PhD, of the Warren Alpert Medical School. “The knowledge gained here opens a door to potential interventions that can enhance teen health moving forward.”