Everything from your workouts to your sleep schedule can affect the number of calories you burn throughout the day. And according to a small new study, there may be a moment of the day when your body naturally burns the most calories.
This is probably due to circadian rhythms, which regulate the internal clock of the body and sleep and wake cycles. These rhythms can also affect the burning of calories, according to the study, which was published on Thursday Current biology. At rest people burn about 10% more calories in the late afternoon than they do late at night, laboratory experiments are found.
That is equivalent to about 130 extra calories burned during the late afternoon and evening versus the middle of the night, without any extra work on your part, says study co-author Dr. Jeanne Duffy, an associate professor of medicine at the Harvard Medical School and a neuroscientist at Brigham and Women & # 39; s Hospital. Even a small increase like this can affect health. "If it happens every day," says Duffy, "you can imagine that this could be right after a while."
Because the research focused on calorie burning at rest – that is, the energy needed to enable bodily functions such as breathing and blood circulation – Duffy says it is unclear whether people should move their workouts and meals around this late afternoon energy boost. What is perhaps more relevant to daily behavior, she says, is to avoid the calorie-burning dip of the body in the late night and early morning.
"Let's say we get up an hour or two hours early and have an hour or two early breakfast," says Duffy. "Perhaps we do not eat that breakfast at a time when our body may not be willing to cope with it, but at a time when we need less energy to maintain our functions, so the same breakfast can result in extra calories stored. because we do not need it to maintain our bodily functions. "
The study included only seven people, so the findings are provisional. But the researchers say that small sample size allowed them to perform extensive laboratory experiments that controlled everything from people's nutrition to their exposure to light and provide unique insights into the natural impact of circadian rhythms.
For 37 days, the men and women in the study (those aged 38 to 69 years) lived in a laboratory without clocks, windows, telephones or the Internet, thereby eliminating environmental inconveniences. The researchers also carefully regulated their sleep and wake times, which meant that they went back four hours every day. These effects threw off the body clocks of the participants and forced their circadian rhythms to work on the basis of internal factors alone, allowing the researchers to observe the true biological morning, noon and night of their bodies, independently of those on the clock. Food intake and activity levels were also defined and monitored by the researchers.
Everyone carried sensors that measure their core temperatures, allowing researchers to measure energy consumption: the higher the core temperature, the more calories the person was burning. They found that the body temperature of people was lowest when circadian rhythms matched late night and early morning, and at their highest about 12 hours later, in the late afternoon.
Duffy says that these findings are of special importance to shift workers and night workers, who often work on unusual schedules. Research has long shown that teamwork is accompanied by a range of health problems, including obesity, type 2 diabetes, cancer and cognitive decline. Duffy says the new study contributes to the idea that these health problems can be associated with disruptions of the circadian rhythm.
Our biological clocks are "timed to be ready for us to do things at regular times of the day and to be optimally functional." When we do things like staying up all night to work, we work against that internal biological clocks, "Duffy explains. "It will not be optimally timed to cope with the fact that you now eat at 3 o'clock in the morning, while we normally do not eat at all at night."
More research is needed to know exactly how these findings affect individuals, but the study contributes to the growing understanding of scientists in the importance of circadian rhythms and their influence on total health.
"This is another metabolic-related function that our body has and that also varies with the time of day," Duffy says. "We have these clocks in us that need to be synchronized and kept in line with our external environment."