Researchers who report in Current biology on November 8th has made the surprising discovery that the number of calories people burn while rest changes with time of day. In rest, people burn 10 percent more calories in late afternoon and early in the evening than in early morning hours.
The find reinforces the important role of the circadian clock in governing metabolism. They also help to explain why irregularities in eating and sleeping schedules due to shift work or other factors can make people more likely to gain weight.
"At the same time, the same thing burned so many calories than does the same at another time surprised us," says Kirsi-Marja Sitting of the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital and Harvard Medical School, author of the magazine.
In order to determine changes over the course of the day in metabolism in addition to the effects of activity, sleep wake cycle and diet, the researchers studied seven people in a special laboratory without any clues about what time it was outside. There were no bells windows , phones or the Internet. Study participants had assigned times to go to bed and wake up. Every night, these hours were adjusted four hours later, that is, they travel west over four time zones every day for three weeks.
"Because they corresponded to circling the world every week, their body's internal clock could not keep up and then it was oscillating at its rate, "coauthor Jeanne Duffy, also in the Division of Sleep and Circadian Diseases at Brigham and Women's Hospital, explains. "This enabled us to measure metabolic rate at all different biological times of the day."
The data showed that the spending on dormant energy is lowest in the circadian, the researchers are designated ~ 0 °, which corresponds to the dip in the core body temperature in the late biological night. Energy consumption was highest at circadian phase ~ 1
The researchers found that the participants' respiratory quotient, which reflects macro nutrient utilization, also varies in circadian phase. This action was at least in the evening and at the peak of the biological morning.
The find offers the first characterization of a circadian profile in fixed resting energy costs and fasting respiratory rate, relaxed from activity effects, sleep wake cycle and diet. In humans, researchers say.
"It's not just what we eat, but when we eat and rest – it affects how much energy we burn or store as fat," says Duffy. "The regularity of habits like eating and sleeping is very important to overall health."
Duffy, Zitting and their colleagues will then look at how appetite and the body's response to food vary with time of day. They also explore how timing, duration and regularity of sleep affect these responses.
Expert discusses the effects of summertime on the body
Kirsi-Marja Zitting et al., Human dormant energy costs vary with the circadian phase, Current biology (2018). DOI: 10,1016 / j.cub.2018.10.005