The human body works around the clock. Our biological functions follow 24-hour cycles, or circadian rhythms, which are physiological and mental changes that are driven by our internal biological clocks. New research explains how we can reset one of these body clocks.
Circadian rhythms are, in turn, governed by so-called master clocks in our brains. The "master clock" is, in fact, a group of intercommunicating nerve cells in the brain, located in an area known as the suprachiasmatic nucleus (SCN).
The SCN has approximately 20,000 neurons and can be found in the brain's hypothalamus, which is a larger brain area that controls body temperature, hunger, and thirst.
New research looks at one of these body clocks and investigates the effect of delayed meal times on the body. Researchers from the University of Surrey in the United Kingdom set out to examine the effect of a 5-hour delay in meal times on the body's master clock, as well as on its several peripheral circadian rhythms.
The first author of the study is Sophie M. T. Wehrens, of the University of Surrey's Faculty of Health and Medical Science.
As Wehrens and colleagues explain, although we know that circadian rhythms, the human metabolism, eating patterns, and nutrition are all interconnected, the link between meal times and the circadian rhythm has not been sufficiently investigated.
The new study is published in the journal Current Biology.
Studying the effect of delayed meal times on the body's biological clocks
Wehrens and team rounded up 10 healthy young men for their experiment, which lasted for 13 days. The participants were served three meals per day, separated by 5-hour intervals, which began either soon or late after waking up. Early meal intervals started half an hour after waking, while late ones began 5.5 hours after waking.
Participants were first used, or "acclimated," to having the meals early, and they were then offset to a schedule of late meals for 6 days.
All of the meals had the same nutritional content and the same number of calories.
Wehrens and team measured the participants' circadian rhythms in a 37-hour "constant routine," which is a special research protocol that specifically enables the scientists to gauge a person's circadian rhythm. Usually, it involves continual bed rest under persistent illumination. In this case, the routine included dim lighting, equally spaced small snacks, reduced physical activity, and no sleep.
Blood sugar levels, gene expression affected by delayed meal times
Overall, the delay in meal time did not have any bearing on the participants' appetite or sleepiness. The brain's master clock was not affected either, as its biomarkers - for example, melatonin and cortisol rhythms, and gene expression - remained unchanged.
However, what did change significantly were the participants' blood sugar levels. Late meal times delayed blood sugar rhythms by an average of 5 hours.
"A 5-hour delay in meal times causes a 5-hour delay in our internal blood sugar rhythms. We think this is due to changes in clocks in our metabolic tissues, but not the 'master' clock in the brain.
We anticipated seeing some delays in rhythms after the late meals, but the size of the change in blood sugar rhythms was surprising. It was also surprising that other metabolic rhythms, including blood insulin and triglyceride, did not change."
Corresponding author Jonathan Johnston, University of Surrey
Additionally, the researchers found that the rhythm of the expression of a gene called PER2 was also delayed by 1 hour. The PER2 gene encodes a key clock component, and its expression was delayed in fat tissue - namely, the researchers noticed an adipose PER2 rhythm delay.
The authors conclude:
"Timed meals therefore play a role in synchronizing peripheral circadian rhythms in humans and may have particular relevance for patients with circadian rhythm disorders, shift workers, and transmeridian travelers."
As the researchers mention, their findings indicate that people who have circadian rhythm problems could try to have meals at specific time intervals to help reset their body clocks.
In particular, such a strategy could be of use to people who work shifts, or those who routinely experience jet lag.