Timing is Everything

By Teresa L. Johnson, MSPH, RD

“A calorie is a calorie, but the body’s physiological response to that calorie might be different depending on the circadian phase the body is exposed to,” said Frank Sheer, PhD, an assistant professor of medicine at Harvard Medical School. Sheer spoke during ASN’s scientific symposium titled “Is ‘When’ We Eat As Important As ‘What’ We Eat?—Chronobiological aspects of food intake.” He opened his discussion by asking why we should care about circadian biology, and then pointed to its possible influence on metabolic processes, meal timing, and disease risk. He explained that an internal “circadian clock”—present in nearly all the body’s cells—regulates the body’s rhythms based on feedback from the brain. We can uncouple those rhythms and choose to be awake, but at a cost, possibly increasing our risk of some chronic diseases, like type 2 diabetes.

Jonathan Johnston, PhD, an associate professor at University of Surrey, “flipped the question on its head,” so to speak, and asked what effect meal timing might have on the body’s internal clock. Johnston explained that circadian rhythms are endogenous and self-sustaining even without external cues, like light and darkness. “Clocks are everywhere,” Johnston said, “and they function like an orchestra.” All the “musicians”—the various clocks—have to be synchronized to function properly, he said. Johnston’s data, gleaned from gene expression studies in human adipose tissue, suggest that modifying meal times might help synchronize the body’s clocks, a possible treatment for the circadian dyssynchrony commonly observed with shift work, jet lag, blindness, and sleep disorders.

“Humans are the only species that disobeys their biological clocks,” said Fred Turek, PhD, a professor at Northwestern University, and the downstream effects might be enormous. We have become “night creatures,” he said, and he and his colleagues are wondering how that affects human health. Turek pointed out that at least 10 to 30 percent of gene expression in the human body is under circadian control including genes in tissues like the brain, liver, and muscle—key players in metabolism—and likely influences disease risk, gut permeability, and the gut microbiota. He suggested that science is at a tipping point with regard to circadian medicine and health, adding that the field of circadian biology is growing and spans many different disciplines, including immunology, oncology, cardiology, and nutrition. “I think it’s the next frontier in medicine,” Turek said.

Jose Ordovás, PhD, a professor at Tufts, explained that circadian rhythms extend beyond 24-hour cycles to monthly and seasonal patterns, a phenomenon now ingrained in human physiology. Ordovás suggested that humans’ ancestral genes were more like the genes of the laboratory animals he studies, which respond to regular cycles of light and dark. Migration away from humans’ equatorial origins likely has altered human circadian biology and, in fact, circadian clocks now vary depending on geographical location. Ordovás speculated on the potential application of circadian biology in personalized or precision medicine as a means to identify those at risk for nutritional disease, and added, “Know your genome and act accordingly.”

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