Despite the “overnight success” of diabetes treatments that have been embraced as weight loss drugs – and for reason – obesity persists as a global public health threat. That includes the rapidly growing prevalence of cardiovascular disease, hypertension, type-2 diabetes, and multiple kinds of cancer. In the United States alone, more than 40 percent of adults and nearly a quarter of kids can be classified as obese. And things aren’t getting any better – despite the skyrocketing success of GLP-1s. One study, for example, predicts “a 33 percent increase in obesity prevalence and a 130 percent increase in severe obesity prevalence over the next [two] decades.”
Now, new data points to a link between the body’s internal clock and our eating habits, revealing that both the circadian system and behavioral cycles exert some influence over our caloric intake.
The researchers, who studied adolescents with a variety of weight statuses, found that overweight (or obese) kids consumed more of their daily calories later in the day compared to those with a healthy weight.
Methodology
“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,” one of the study’s authors, Frank A.J.L. Scheer, PhD, a professor of Medicine at Brigham and Women’s Hospital, explained. “This study is the first to demonstrate that food intake itself is regulated by our internal body clock.”
The researchers want to parse out the influence of the body’s internal circadian timing system and external behavioral factors such as sleep/wake and fasting/eating cycles. The team worked with a Forced Desynchrony protocol, in which participants adhered to an altered sleep/wake schedule under controlled lighting conditions.
Over seven 28-hour sleep/wake cycles, 51 male and female adolescents — classified as either at healthy weight, overweight, or obese — lived in an environment where the researchers could minimize external influences on circadian rhythms, such as natural light.
By structuring meal timing across different circadian phases, the researchers managed to pinpoint the circadian system’s independent role in governing food intake. The study revealed that caloric consumption naturally fluctuates across the circadian cycle, peaking in the evening.
The strength of this pattern varied by weight status. Overweight and obese participants, for example, showed a blunted response to circadian-driven hunger cues.
How the Circadian System Affects Eating Patterns
The research confirmed that the circadian system plays a huge role in dictating caloric intake, with participants generally consuming more calories later in the cycle. The circadian rhythm of caloric intake showed a peak-to-trough variation of about 196 kcal per meal, with the highest intake occurring around 5:30 p.m. This timing aligns with earlier research on hunger and appetite regulation, bolstering the proposition that the body’s internal clock ramps up the drive for food as the day wears on.
Even so, overweight or obese adolescents consumed a greater share of their daily calories even later in the day – compared to their healthy-weight counterparts. On average, their peak caloric intake occurred about one hour later in the circadian cycle.
On top of that, the participants showed a lower amplitude in their circadian-driven eating patterns, which hinted that their eating habits operated more independently from their body’s natural signals.
Behavioral Cycles and Their Role in Eating Patterns
Beyond the circadian system’s influence, the research team also wanted to explore how behavioral cycles — such as meal timing relative to waking — influence caloric intake. Across all weight groups, people ate their largest meal of the day after the longest fasting period (roughly 13 hours). Participants consumed an average of 725 kcal during this meal, with calorie consumption tapering off with each subsequent meal.
However, those living with obesity displayed a less distinct eating pattern that included less variation in intake throughout the day. This also included consuming more calories during later meals.
These findings contrast with naturalistic studies where breakfast tends to be the smallest meal of the day. Researchers suggest that the extended fasting period in this controlled setting could have amplified the behavioral cycle’s effect on meal size.
Additionally, in real-world settings, external factors such as social influences, school schedules, and light exposure might be interacting with circadian and behavioral rhythms.
Implications for Weight Management
“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,” the study’s lead investigator, Mary A. Carskadon, PhD, with the Warren Alpert Medical School, said. “The knowledge gained here opens a door to potential interventions that can enhance teen health moving forward.”
Encouraging at-risk individuals to pair up their eating habits with their natural circadian rhythms could help reduce the likelihood of overeating later on. Strategies such as front-loading calorie intake earlier, while maintaining consistent meal timing through the day could help.
The paper’s authors suggest that future research could target the biological mechanisms underlying the reduced circadian influence on caloric intake in individuals with obesity. Factors such as hormonal regulation of hunger, neuroendocrine responses, and genetic predispositions might all have a part to play.
Additionally, studies examining real-world influences on eating behaviors — such as light exposure, social environments, and cultural norms — could offer further insights.
This study provides compelling evidence that no single system governs our caloric intake. The body’s internal clock – along with external behavioral cycles – work together in shaping when (and how much) we eat.
As obesity rates keep climbing, understanding how circadian rhythms shape our eating behaviors could pave the way for better interventions. By aligning meal timing with the body’s natural rhythms, individuals might improve long-term health outcomes.
Further Reading
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