Researchers from Harvard Medical School recently conducted a small study, published in Current Biology journal, to determine how circadian rhythms, which control the body’s sleep cycles, influence calorie burning.
To do so, they examined adults, aged 38 to 69, in a special laboratory without clocks, windows, phones and Wi-Fi to hide the time of day. The participants had assigned bedtimes and wake-up times. Each night, those times were adjusted four hours later to reflect the different time zones. This method helped the scientists identify the subjects’ natural circadian rhythms without the influence of environmental factors.
“Because they were doing the equivalent of circling the globe every week, their body's internal clock could not keep up, and so it oscillated at its own pace,” co-author Jeanne Duffy explained in a statement. “This allowed us to measure metabolic rate at all different biological times of day.”
The analysts also tracked the participants’ food intake, activity levels and body temperatures, which helped the team measure energy expenditure.
After analyzing the results, they said people’s body temperatures were lowest late at night and early in the morning, and at their highest was in the late afternoon. They revealed the higher the temperature, the more calories burned.
In fact, they discovered individuals naturally burn about 10 percent more calories, which equals about 130 calories, in the late afternoon than they do late at night.
“It is not only what we eat, but when we eat – and rest – that impacts how much energy we burn or store as fat,” Duffy said. “Regularity of habits such as eating and sleeping is very important to overall health.”
Despite the findings, the researchers are not sure if people should reschedule their workouts and mealtimes. However, they hope to further their investigations so that they can evaluate how the body's response to food varies with the time of day.
Want to learn more about the assessment? Take a look here.