Washington DC: Did you know! Your eating and sleeping patterns regulate the amount of calories you burn.
Researchers found that resting people burn 10 percent more calories in the late afternoon and early evening than in the early hours of the morning.
The results were published in the journal Current Biology.
They reinforce the important role of the circadian clock in controlling metabolism. They also help to explain why eating and sleeping irregularities due to shift work or other factors make people more likely to gain weight.
"The fact that the same thing burned so much calories at one time of the day than doing the same thing at a different time of the day surprised us," said lead author Kirsi-Marja Zitting of Harvard Medical School.
To identify changes in the course of the day along with the effects of activity, sleep-wake cycle, and diet, the researchers looked at seven people in a specialized lab with no indication of what time it was outside. There were no clocks, windows, phones or internet. The study participants had set times to go to bed and wake up. Each night, these times were adjusted four hours later. This equates to a three-week trip across four time zones to the west.
"Because they wanted to circle the globe every week, the internal clock of their bodies could not keep up, and so it oscillated at their own pace," said co-author Jeanne Duffy. "This allowed us to measure the metabolic rate at all different biological times of the day."
The researchers found that the respiratory quotient of the participants, which reflects the use of macronutrients, also varies in the circadian phase. This measure was lowest in the evening and highest in the biological morning.
The results provide the first characterization of a circadian profile in terms of energy consumption and accelerated respiratory quotient, which is decoupled from the effects of activity, the sleep-wake cycle, and diet in humans.
"It's not just what we eat, but when we eat – and rest – it affects how much energy we burn or store as fat," Duffy said. "The regularity of habits such as eating and sleeping is very important for general health."