A new study reveals a distinct relationship between circadian rhythms, weight, and eating habits in teenagers.
The research, co-led by Mary Carskadon, PhD, a professor of psychiatry and human behavior, found that adolescents classified as overweight or obese consumed more calories later in the day compared to participants with healthy weights.
“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 Carskadon, who directs the Bradley Hospital Sleep Research Laboratory. “The knowledge gained here opens a door to potential interventions that can enhance teen health moving forward.”
The circadian system is composed of trillions of “clocks” present in virtually all organs, tissues, and cells, which prepares biology and behavior to adapt 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.
Previous studies have analyzed sleeping and eating behavior using measures of self-reported hunger and other variables, says coauthor David Barker, PhD, an associate professor of psychiatry and human behavior (research). Some factors that set this study apart, he says, were the meticulous measuring of food before and after meals and the fact that environmental and behavioral influences were controlled for while the participants remained in the lab.
Fifty-one volunteers between the ages of 12 and 18 participated in the study, and were divided into three groups based on body mass index. They were placed on 28-hour sleep and wake cycles and remained in the same space throughout the 11-day study. To control for outside influences on circadian rhythm, researchers removed all external time cues, including clocks and access to natural light. Researchers tracked the food that was eaten as well as caloric intake.
The results, which were published in PNAS, showed that changes in the circadian system throughout the day and night significantly influenced food consumption. In all three groups, food intake peaked in the late afternoon and early evening and was lowest in the morning, demonstrating that the body’s biological clock directly impacts how much people eat at different times of the day.
Participants in the obesity and overweight groups consumed significantly more calories in the 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.
Carskadon says the findings could inform clinicians counseling teens on ways to manage their weight.
“For example, the influence of circadian timing could be influenced by excluding light late in the day and enhancing bright light in the morning, especially while exercising,” she says. “That might help pull the rhythms to a better place—and also create healthy habits.”