Eating times affect circadian rhythm, study finds

Biological Clocks
Photo by Karen Tian.

Researchers at the Yale School of Medicine have found that when and what you eat affects the synchronization of the body’s biological clocks.

Biological clocks, which are found in every cell of the body, operate on a 24-hour cycle, according to a preview of the study written by Gerald Hart, biological chemistry professor at Johns Hopkins University. Synchronizing all the clocks in the body is essential for the body to function at its best. The three-year study, which was conducted on lab mice, found that eating at certain times of the day, which vary depending on one’s sleep habits, may lead to optimal body functionality via clock synchronization. The findings were published Feb. 5 in the journal Cell Metabolism.

When food is consumed at the optimal times of the day, the body’s peripheral clocks, which are found in every cell outside the brain, synchronize with the body’s central clock, which is located in the brain and responds to external signals like light and temperature, said researcher Xiaoyong Yang, assistant professor of comparative medicine and of cellular and molecular physiology. Although the central clock, or “master clock,” controls the peripheral clocks, only the latter respond to the “feeding and fasting cycle,” Yang said. This cycle characterizes “fasting” as any time the stomach is empty.

In the morning, your central clock responds to the light, Yang said. “But if you don’t eat, and you fast, the peripheral clocks respond to that,” creating a dyssynchrony between the clocks, he added. Ueli Schibler, professor of molecular biology at the University of Geneva, said mice with this dissynchrony appear ill, and are not as “active or energetic” as those with synchronous cycles.

The study also showed that eating at the right times can help protect from disease. Past research has shown that women involved in shift work — especially rotating shift work, in which people work during the day one week and during the night the next — have an increased risk of cancer, the study’s lead researcher Min-Dian Li GRD ’15 said. Rotating shift workers are more likely to have dissynchronous body rhythms, increasing their likelihood of becoming diabetic, obese or depressed, Yang said.

“It seems pretty clear that the long-term disruption of circadian rhythms is pretty harmful,” Schibler added.

Both Li and Yang said eating two meals per day may be most beneficial for the synchronization of biological clocks — this advice stands in contrast to findings from nutritional studies showing that eating in small amounts frequently can help with weight control.

For those who wake up early in the morning, eating breakfast and lunch and skipping dinner is best for circadian rhythm synchronization, Yang said. Night owls should eat lunch and dinner as their two meals, he added.

Paolo Sassone-Corsi, biological chemistry professor and director of the Center for Epigenetics and Metabolism at University of California, Irvine School of Medicine, said the study does not definitively state the day’s optimal eating times, as it solely focuses on glucose. He said understanding how various types of nutritional intakes affect the clock system will be an “important step forward.”

Yang said the next step for the team will be to look at the effect eating proteins has on synchronization. He also said that, with more funding, the team would like to conduct the same research in humans.

The study was funded by the National Institutes of Health, the American Diabetes Association and the Ellison Medical Foundation.

Correction: March 6 

A previous version of this article misattributed the finding that unhealthy foods eaten at certain times of the day may have little impact on health to the study by researchers at the School of Medicine. In fact, that finding came from an earlier study conducted by Dr. Satchin Panda of the Salk Institute for Biological Studies.

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