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Everything from your workouts to your sleep schedule can affect how many calories you burn during the day. And according to a recent study, there may be a time of day when your body naturally burns more calories.
This is probably due to circadian rhythms, which control the body's internal clock as well as sleep and standby cycles. These rhythms can also affect the burning of calories, according to research published Thursday in Current biology. At rest, humans burn about 10% more calories in the late afternoon than after dark, according to laboratory experiments.
That equates to about 130 extra calories burned late in the afternoon and into the evening compared to the middle of the night with no extra work on your part, says Dr. Jeanne Duffy, co-author of the study. , Associate Professor of Medicine at Harvard Medical School and Neuroscientist. at Brigham Hospital and Women's. Even a small increase like this could have an impact on health. "If this happens everyday," says Duffy, "you can imagine that this could build up over time."
Since research has focused on calorie expenditure at rest, that is, the energy needed to fuel bodily functions such as breathing and blood circulation, Duffy says it's not clear if people should postpone their workouts and meals around this energy surge at the end of the day. According to her, what is perhaps most relevant for daily behavior is to avoid the calorie bath burning the body late at night and early in the morning.
"Suppose we got up an hour or two earlier and had breakfast an hour or two earlier," says Duffy. "We may be having breakfast not only at a time when our body may not be ready to bear it, but at a time when we need less energy to maintain our functions. Therefore, the same breakfast could result in extra stored calories because we do not need those calories to maintain the functions of our body. "
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The study included only seven people, so the results are preliminary. However, the researchers explained that the small size of their sample allowed them to conduct many laboratory experiments ranging from people's diets to exposure to light, providing a unique insight into the natural impact of circadian rhythms.
For 37 days, men and women in the study (ages 38 to 69) lived in a laboratory without a clock, window, phone or internet, eliminating environmental disturbances. The researchers also carefully regulated their sleep and waking hours, rolling them back four hours a day. These effects hindered participants' body clocks and forced their circadian rhythms to operate based solely on internal factors, allowing researchers to observe the biological reality of their bodies, morning and afternoon, separately from those on the body. clock. Levels of food consumption and activity were also defined and monitored by the researchers.
Each carried sensors that measured the temperature of his body, allowing researchers to measure energy expenditure: the higher the temperature, the more calories were burned. They found that body temperatures were at their lowest when the circadian rhythms were late night and early morning, and at their peak about 12 hours later in the late afternoon.
Duffy says these results have special significance for shiftworkers and night workers, who often work on unusual schedules. Research has long shown that shift work is associated with a range of health problems, including obesity, type 2 diabetes, cancer, and cognitive decline. Duffy says the new study adds to the idea that these health problems may be associated with circadian rhythm disturbances.
Our biological clocks are "programmed to be ready for operation at regular times of the day and to work optimally. When we do things like staying up all night at work, we work against these internal biological clocks, "says Duffy. "It will not be time to deal with the fact that you are eating now at 3 in the morning, whereas normally we do not eat at all during the night."
More research is needed to know exactly how these findings affect individuals, but the study adds to scientists' growing understanding of the importance of circadian rhythms and their impact on overall health.
"It's another metabolic function of our body that also varies with the time of day," says Duffy. "We have these clocks inside of us that need to be synchronized and kept in step with our external environment."
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