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The human body burns up to a 10% more calories at the end of the afternoon this first thing in the morning when the metabolic rate is lower. This is the main conclusion of a study analyzing the effects of circadian rhythm on human metabolism.
Posted in the magazine Current biology Research shows that energy expenditure depends not only on diet, physical exercise and the number of hours of sleep, but also on the body clock. According to a study conducted by researchers at Brigham and Women's Hospital in Boston, the resting metabolic rate, which is 60% and 70% of energy expenditure daily in the most sedentary adults, varies according to the circadian rhythm.
Regularity of habits
"It's not just what we eat, but eating and resting affects us energy we burn or keep the body in fat, "says researcher Jeanne Duffy, co-author of this study. "The regularity of habits such as eating or sleeping is very important for health."
For researchers, the fact that the circadian rhythm has an influence on the metabolism is relevant because it could explain why people with irregular sleep schedules are more likely to gain weight.
Although energy expenditure has already been measured throughout the day in previous studies, the peculiarity of this research is that the circadian rhythm has been analyzed separately from the effect of other variables, such as consumption or metabolism. dream – in the metabolism.
For this purpose, the specialists examined, during three weeks, seven patients on a special laboratory in which there were no clocks, no windows, no telephones, no internet. In this way, the participants could not know what time it was abroad and their biological clock could not be guided by environmental factors
In addition, participants assigned hours to go to bed and wake up, which changed constantly. Specifically, the schedules were delayed by four hours each night, which is equivalent to traveling each day in the west over four time zones.
"Being able to measure all the different circadian cycles during the 24 hours of the day, with the same twelve-hour period rest and rest among them, we had to manipulate the relationship between the dream and the biological clock. Normally, the two follow the same rhythm one with respect to the other. It is therefore impossible to measure the resting metabolic rate under the same conditions and at different times of the day, "the researcher told SINC.
Internal clock
"As they were doing the equivalent of going around the Earth every week, their body's internal clock could not keep up, and it was oscillating at their own pace," says Duffy. "It allowed us to measure the metabolic rate at different biological times of the day."
According to the results, the moment of the lowest energy expenditure corresponds to the circadian phase ~ 0 °, period in which, for our body, it is early morning because there is a temperature drop in the abdomen. On the contrary, the body burns more calories in the ~ 180º phase, which takes place about 12 hours later, which would be biologically the end of the afternoon.
They also found that patients' respiratory quotient, which is used to measure metabolic rate because it reflects macronutrient expenditure, also varies with circadian phases. This measurement was lower in the late afternoon and higher in the biological morning.
According to experts, the next line of study will focus on how the appetite and the body respond to different varieties of food depending on the time. They also examine the influence of the timing, duration and regularity of sleep on body responses.
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