When you eat matters as much as what you eat

Circadian rhythms have a profound impact on many aspects of our health, from sleep to metabolism.

The diet we establish in childhood and adolescence can lay the foundation for lifelong health, but weight gain and obesity are commonly blamed on poor diet and lack of exercise alone, without considering the impact of circadian rhythms.

New research indicates that when we eat is as critical as what we eat. Researchers are beginning to understand how our own biological clock controls hunger and fullness.

The body clock and weight gain

A team of researchers from Warren Alpert Medical School and Mass General Brigham set out to investigate the intricate relationship between circadian rhythms, metabolism, and overall health.

The experts focused on adolescents, a group particularly susceptible to developing long-term health concerns based on their eating behaviors.

The researchers uncovered a correlation between overweight or obese adolescents’ caloric consumption and the timing of their meals.

They found that youngsters with higher body-mass indexes tended to consume a larger portion of their daily caloric intake later in the day when compared to their peers with healthier weights.

Lead investigator Mary Carskadon, a professor of psychiatry and human behavior at Warren Alpert, shared her observations.

“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.

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

Circadian rhythms: A hidden force in nutrition

Our circadian system is essentially a network of countless “clocks” present in almost every part of our body. These clocks help us adapt to changing demands throughout the day and night.

However, this system varies from one person to another due to multiple factors including genetics, behavior, and environmental influences.

The uniqueness of this study, according to contributing author David Barker, lies in the precise measurement of food intake and the control of environmental and behavioral influences.

The study was carried out in a controlled environment, in the absence of any external time cues, to ensure that the outcomes reflected only the circadian influences on eating behaviors.

The experiment and its findings

A group of 51 volunteers, aged 12 to 18, participated in the study. They were divided into three groups based on their body mass indexes.

The experiment was designed to maintain a 28-hour sleep and wake cycle, slightly longer than a typical 24-hour day.

The teenagers lived in the same space for 11 days and 10 nights, under carefully managed light settings. Provided with six opportunities to eat at fixed times, they were free to consume as much as they wished.

The researchers monitored the food intake and caloric count closely. Interestingly, the results showed that those in the overweight or obese groups ate more of their daily calories in the afternoon and early evening, when compared with the participants in the healthy weight group.

This indicates that our inner biological clock greatly influences our eating patterns, and that the timing of eating may affect our tendency to gain weight.

Frank Scheer, director of the Medical Chronobiology Program at Brigham and Women’s Hospital, highlighted the significance of the study.

“This study is the first to demonstrate that food intake itself is regulated by our internal body clock,” said Scheer.

Harnessing the power of circadian hythms

Carskadon believes that insights like these could be incredibly useful in designing weight management strategies for adolescents.

“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. That might help pull the rhythms to a better place – and also create healthy habits,” she explained.

The research team plans to explore the connection between our circadian system, diet, and metabolism, and how this knowledge could potentially help design timed dietary interventions to promote healthier lifestyles.

By identifying the optimal windows for eating, based on individual circadian rhythms, future strategies could help curb obesity risks before they take root.

The full study was published in the journal Proceedings of the National Academy of Sciences.

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