At the AAST 2019 annual meeting, Frank Scheer, PhD, shared medical chronobiology research insights with an audience of sleep technologists.

As the rates of preventable diseases have skyrocketed over the last 20 years in the United States, it is easy to place the blame on rapid changes in lifestyle, diet, and exercise, but what if there is another less obvious culprit wreaking havoc on our biological systems?

Frank Scheer, PhD, professor of medicine at Harvard Medical School and director of the medical chronobiology program at Brigham and Women’s Hospital in Boston, says disruption of the body’s circadian rhythms may be one major reason why more Americans are living with preventable diseases. During his keynote talk at the 2019 AAST annual meeting in St. Louis, he outlined how recent research supports the hypothesis that higher rates of shiftwork and other forms of nighttime disruption could be contributing to increased rates of obesity, diabetes, and other common ailments.

When people are awake during the night, their behaviors are often mismatched with their internal body clocks. This can lead to nighttime eating, which can influence the way the body processes sugar and could lead to a higher risk in diabetes. “What happens when food is eaten when you normally should be fasting?” Scheer asked the audience. “What happens is that your glucose tolerance goes out the window….So your glucose levels after a meal are much higher.” This can increase people’s risk for diabetes.

With the rise of personal electronic devices, more people are also staying awake later into the night to the glow of an e-book reader or smartphone. Even streetlights can emit the blue light that may disrupt the body’s internal master clock, the suprachiasmatic nuclei (SCN), a small group of neurons in the brain that sit near the crossing of the optic nerves in the hypothalamus.

Nearly every biological system in our bodies runs on this internal clock, regulated at least in part by sunlight. In recent decades there has been more disruption to these systems than ever before, Scheer explained.

Peripheral internal clocks, which are regulated by the SCN, may be individually sensitive to outside cues such eating.

“You can disassociate the liver clock from the central clock. For example, the central clock could live on St. Louis time, but your liver might be in Tokyo,” Scheer said. “Even within one organ, like the liver, you can have different neighboring cells that live in different time zones all at the same time.”

The Importance of Food Timing on Health: If a Calorie is a Calorie, Why Would it Matter When You Eat it?

Research has shown that sleep restriction could also negatively impact the body’s ability to process sugar. A study from the University of Chicago School of Medicine found that insufficient sleep may disrupt fat metabolism and reduce insulin’s ability to regulate blood sugars, according to the research published in Diabetologia, the journal of the European Association for the Study of Diabetes.

“At the population level, multiple studies have reported connections between restricted sleep, weight gain, and type 2 diabetes. Experimental laboratory studies, like ours, help us unravel the mechanisms that may be responsible,” Esra Tasali, MD, assistant professor of medicine at the University of Chicago and senior author of the study, says in a statement.

In a separate study, Scheer partnered with Marta Garaulet, PhD, MPH, from University of Murcia in Spain, to ask the question: Is there also an association between when people eat and weight loss?

“What we found is that early eaters lost about 25% more during the same intervention,” he said, which suggests that a calorie is metabolized differently in the morning than in the evening.

The research found that late-eaters experience a slower weight-loss rate than early-eaters. Late-eaters also lost fewer pounds overall than earlier-eaters, which suggests that the timing of meals could be an important factor in weight loss programs, according to the study published in the International Journal of Obesity. 

In another study, researchers looked at meal timing in college students in relation to their degree of obesity and found that those who ate at a late circadian phase had a higher body mass index and higher adiposity, according to the work published in the American Journal of Clinical Nutrition. Lead author Andrew McHill, PhD, now a research assistant professor at Oregon Institute of Occupational Health Sciences, collected data on 110 college students over 30 days.

“[The results suggest] that the timing of food intake relative to our internal circadian system is what is most important,” says Scheer. “For obesity, we think that the time of food intake is very important, it is not just what you eat, it is when you eat.”

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Lisa Spear is associate editor of Sleep Review.