Calories burnt at rest depends on time of day,finds study

A new of its kind study published in the journal Cell Biology reports that the number of calories people burn while at rest changes with the time of day.

The findings signify the importance of the circadian clock in regulating metabolism. They also help to explain why irregularities in eating and sleeping schedules due to shifting work or other factors may make people more likely to gain weight.

The study revealed that people burn 10 percent more calories in the late afternoon and early evening than in the early morning hours when at rest.

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"The fact that doing the same thing at one time of day burned so many more calories than doing the same thing at a different time of day surprised us," says Kirsi-Marja Zitting, the lead author of the study.

The researchers conducted a study to determine changes over the course of the day in metabolism apart from the effects of activity, sleep-wake cycle, and diet. The researchers studied seven study participants under study in a special laboratory had no clues about what time it was outside. There were no clocks, windows, phones, or Internet. Study participants had assigned times to go to bed and wake up. Each night, those times were adjusted four hours later, the equivalent of traveling westward across four time zones each day for three weeks.

"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," said co-author Jeanne Duffy.

The key study findings included in the study are:

• The data showed that resting energy expenditure is lowest at the circadian phase the researchers designated as ~0°, corresponding to the dip in core body temperature in the late biological night.


• Energy expenditure was highest at circadian phase ~180°, about 12 hours later, in the biological afternoon into evening.


• The researchers found that participants' respiratory quotient, which reflects macronutrient utilization, varies by circadian phase, too. This measure was lowest in the evening and highest in the biological morning.

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"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 says. "Regularity of habits such as eating and sleeping is very important to overall health."

For reference log on to https://doi.org/10.1016/j.cub.2018.10.005