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Contemporary science can explain many of our bodily processes, but it struggles to understand how our metabolisms change or how we burn calories throughout the day. One of the problems is that it is extremely difficult to isolate the impact of our natural circadian rhythms on those of the "clock time", the models of the day built by society. So a group of scientists did what scientists do: create a totally crazy experiment to isolate the variables.
In fact, in a new study, scientists – a group from Harvard Medical School, Brigham and Women's Hospital, and Penn State University – literally isolated their subjects from the world. For 37 days, the 10 men and women who agreed to participate in the study lived in a laboratory without a window, clock, phone or internet. Presumably, they had a lot of reading material.
The results showed that the body's resting metabolism fluctuates with our circadian rhythms: the internal cycle of hormones that tells us less when we should be getting ready for bed and when we wake up, among other things. The participants' internal temperatures were highest, that is, they burned the most calories during the biological afternoon of their body and burned the least during the biological night. As fast as possible, the body burns about 130 calories more than the slowest.
The researchers worked with 10 healthy volunteers, five men and five women aged 38 to 69 years. (All women were menopausal, it was useful, menstrual cycles can also affect the circadian rhythm (paywall)). Some volunteers repeated the experiment, so the researchers finally completed 13 separate trials.
In six trials, participants went to bed and woke up regularly, sleeping at night for 8 to 10 hours on a regular basis. But in the other seven trials, the researchers extended the participants' day by about four hours, which amounts to flying to a time zone behind you. "As they were doing the equivalent of going around the world every week, the internal clock of their body could not keep pace and therefore oscillated at its own pace," said Jeanne Duffy, neurologist at Harvard Medical School and principal author. paper, said in a statement.
The researchers measured their central body temperature rectally (another non-experimental aspect of the experiment). Higher body temperatures mean that more calories are burned. Over time, the seven volunteers in the experimental group had the lowest internal temperatures around the "night" of their circadian rhythms. If they had a 24-hour schedule, it would be in the middle of the night and early morning. They burned the most calories 12 hours later, usually around the afternoon and the first hours of the evening. If you imagined these fluctuations as a wave, at the peaks, they burned about 55.2 calories more per hour than nadirs, which means that resting bodies burned about 10% more in the afternoon and in the evening than the day before. early in the morning.
Duffy told Time that our body works best when our sleep and meal schedules are consistent. "When we do things like staying up all night at work, we work against these internal biological clocks," she said. Eating late at night (or very early in the morning) could contribute to weight gain, as our bodies do not burn as many calories at this stage as they do at other times in the 24-hour daily cycle.
Much remains to be done to explain the relationship between circadian rhythms and metabolism. This study was small and focused only on resting metabolisms – the energy we need to be awake, breathe and pump blood. But this paves the way for future work to understand why people with irregular sleep patterns, such as shift workers or people who are prone to sleepless nights, are more likely to gain unwanted weight.
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