Blame the clock
By Brown University
However, a new study from the Warren Alpert Medical School
of Brown University and Mass General Brigham has identified a strong connection
between circadian rhythms, weight, and eating behaviors in adolescents. This
age group is particularly important because their eating patterns can have
long-term health implications. The study found that adolescents classified as
overweight or obese consumed more calories later in the day compared to those
with a healthy weight.
Circadian Rhythms and Their Role in Eating Behavior
According to lead investigator Mary Carskadon, a professor
of psychiatry and human behavior at Brown University, these findings highlight
the significant role circadian rhythms play in influencing late-day calorie
intake, particularly in individuals at higher risk for obesity.
“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
Carskadon, who also 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 results were published in the Proceedings
of the National Academy of Sciences.
Understanding the Body’s Internal Clock
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, said study author
David Barker, an associate professor of psychiatry and human behavior
(research) at Brown. Some factors that set this study apart, Barker said, 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.
A Controlled Environment: No Clocks, No Light, Just
Science
Fifty-one volunteers between the ages of 12 and 18
participated in the study, which was conducted at the Bradley Hospital Sleep
Research Laboratory. Participants were divided into three groups based on body
mass index. They were placed on 28-hour sleep and wake cycles — slightly longer
than a typical 24-hour day — and stayed in a controlled dim-light setting while
awake and in complete darkness during sleep.
Participants remained in the same space throughout the
study, which lasted for 11 days and 10 nights. To control for outside
influences on circadian rhythm, researchers removed all external time cues from
the lab’s environment, including clocks and access to natural light.
Participants received six opportunities to eat at fixed
times across the wake episode, with a standardized menu and could consume as
much food during the meal as they wanted. Researchers tracked the food that was
eaten as well as caloric intake. During the day, they were monitored by student
research apprentices from Brown University and other institutions, who offered
opportunities to join in a variety of activities including making crafts,
watching movies (with screen lights dimmed), and playing social games.
Late-Night Calories and the Circadian Clock’s Influence
The results 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, even after accounting for behavioral and
environmental factors, demonstrating that the body’s biological clock directly
impacts how much people eat at different times of the day.
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.
According to study author Frank Scheer, director of the
Medical Chronobiology Program at Brigham and Women’s Hospital, it was already
well-known that the circadian system affects hunger and metabolism. What
remained unclear, he said, was whether the circadian system — when isolated
from influences of environmental and behavioral cycles, including light, sleep,
and activity cycles — directly influences food consumption.
“This study is the first to demonstrate that food intake
itself is regulated by our internal body clock,” Scheer said.
Shaping the Future: Circadian Rhythms and Weight
Management
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.
Carskadon said that the findings like those from the study
could inform clinicians counseling adolescents 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,” Carskadon said. “That might help pull
the rhythms to a better place — and also create healthy habits.”
With future research, the team aims to gain a deeper
understanding of the interactions between the circadian system, diet, and
metabolism, as well as the mechanisms underlying these relationships, and the
implications for developing timed dietary interventions to improve health.
Reference: “Independent effects of the human circadian
system and sleep/eating cycles on caloric intake in adolescents vary by weight
status” by Barker, D. et al., 17 February 2025, Proceedings
of the National Academy of Sciences.
DOI: 10.1073/pnas.2407907122
The research was supported by the National Institute of
Diabetes and Digestive and Kidney Diseases (R01 DK101046), the National Heart,
Lung, and Blood Institute (R01HL153969), the National Institutes of Health (R01-HL140574,
R01-HL153969, R01-HL167746, R01-HL164454) and the COBRE Center for Sleep and
Circadian Rhythms in Child and Adolescent Mental Health funded by the National
Institute of General Medical Sciences (P20GM139743).
