When men postpone meal times, it delays one of the body's clocks, British researchers say, a finding that sheds light on a potential way to overcome jet lag and health harms for shift workers.
Our bodies run a roughly 24-hour cycle called the circadian or sleep/wake rhythm. It is controlled by a master "clock" in the brain that responds to light signals from the retina, synchronizing other clocks throughout the body.
Now investigators have discovered that a five-hour delay in meal time causes a five-hour delay in blood glucose rhythms.
"We think this is due to changes in clocks in our metabolic tissues but not the 'master' clock in the brain," said Jonathan Johnston of the University of Surrey, one of the authors of the study published in Thursday's issue of the journal Current Biology.
"This work is important because it demonstrates for the first time that a relatively subtle change of standard human feeding pattern re-synchronizes key metabolic rhythms in the body."
Currently, people disoriented by the sluggish time warp of jet lag may take melatonin supplements and time their light exposure to help synchronize their clocks.
While the study introduces the idea of adding meal timing to the clock reset toolkit, the practical details of how to do so still need to be worked out.
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In the experiment, 10 healthy young men came to a specialized sleep lab for 13 days.
At first, breakfast was set for 30 minutes after waking. Then, after the men got used to eating early, they switched to a meal served five hours later.
The men stayed in a room with constant dim lighting and ate identical small, hourly snacks for 37 hours while maintaining the same body posture.
Ticking blood-sugar clock
The researchers took a series of blood samples and biopsies that were tested for a suite of measures including blood glucose, insulin (the hormone that regulates glucose), a major type of fat, as well as two markers of the brain's master clock, melatonin and cortisol.
"We anticipated seeing some delays in rhythms after the late meals, but the size of the change in blood glucose or sugar rhythms was quite surprising," Johnston said.
Key regulators of human circadian rhythms, the light-dark and sleep-wake cycles, didn't change. Neither did other metabolic indicators such as blood insulin concentrations.
Only glucose rhythms shifted with the five-hour meal time.
Despite the small number of participants, the design of the study and results are convincing, said neuroscientist Prof. Frank Scheer, director of the medical chronobiology program at Brigham and Women's Hospital in Boston. He was not involved in the research.
"This is a very important finding in the circadian field, because to date, there had been no convincing data that meal timing can change the timing of circadian rhythms in metabolic measures in humans," Scheer said.
The study suggests that meal timing can indeed be effective in synchronizing a body clock, Scheer said.
"This work suggests that it is not only important to think about light in resynchronizing body clocks in shift workers and on long-haul flights across time zones, as is classically done, but also to thinking about meal timing."
Whether the findings translate to healthy women or patients will need to be studied in the real world as opposed to the lab.
From a health perspective, the goal of meal timing is likely to be most relevant to shift workers who make up about 20 per cent of the work force in many countries, and patients with circadian rhythm disorders, Johnston said.
Having body clocks that are out of whack in the long term is thought to increase the risk of Type 2 diabetes and cardiovascular disease.
The study was funded by the UK Biotechnology and Biological Sciences Research Council.