The human body works according to a roughly 24-hr cycle. It is controlled by a master clock in the brain and by peripheral clocks in other parts of the body, which are synchronized according to external cues such as light. According to a report in Current Biology on June 1, at least one of these clocks can also be reset based on what time an individual eats breakfast, lunch, and dinner.
Researchers said that the findings recommended that regular mealtimes might help people to keep their clocks on the same time.
"A 5-hour delay in meal times causes a 5-hour delay in our internal blood sugar rhythms," says Jonathan Johnston of the University of Surrey. "We think this is due to changes in clocks in our metabolic tissues, but not the 'master' clock in the brain."
Researchers knew that the clock system of the body and metabolic control were closely associated. Studies had also shown that circadian rhythms respond to meals. Yet, the researchers explained that it has only recently become possible to study relevant markers of the many clocks of the human body, both inside and outside the brain.
In the new study, Johnston, along with Sophie Wehrens and their colleagues, enrolled ten healthy young men in a 13-day laboratory protocol. The men ate three meals at 5-hr intervals and all the meals had the same calorie and macronutrient content.
Each participant started with a mealtime set to 30 minutes after waking, and then, after getting used to eating early, they switched to a 5-hr delayed meal for 6 days. After each meal schedule, the circadian rhythms of the participants were measured in a 37-hr constant routine. The routine included dim lighting, small hourly snacks, limited physical activity, and no sleep.
The mealtime change did not seem to have an effect on hunger or sleep among the participants. No change was observed in the markers of the brain's master clock, such as melatonin and cortisol rhythms, or clock gene expression in the blood. Nevertheless, the researchers discovered that later mealtimes significantly affected the blood sugar levels as the blood sugar rhythms were delayed by more than 5 hrs on average after later meals.
"We anticipated seeing some delays in rhythms after the late meals, but the size of the change in blood sugar rhythms was surprising," Johnston says. "It was also surprising that other metabolic rhythms, including blood insulin and triglyceride, did not change."
The research team has also found that the rhythmic expression of a gene-PER2, which encodes a core clock component was delayed in fat tissue by about an hour. The findings revealed that mealtimes regulate the molecular clocks in individuals and that the shifts could support blood sugar level changes.
The findings recommended that people who have difficulty with circadian rhythm disorders, such as people working in shifts and those on long-haul flights, might consider timed meals as part of an overall strategy to help resynchronize their circadian rhythms. The researchers said that this would be important to learn more about the consequences on health, as now the influence of mealtimes on human metabolic rhythms is clearer.