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At this time of day, we burn the most calories

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How many calories we burn at any one time depends not only on what we are doing, but also on what time it is.

In the afternoon we can taste pancakes and sandwiches with a better conscience than for breakfast - because in the late afternoon and early evening, our energy consumption is highest, shows a recent Harvard study.

 "The fact that the same activity burns so much more calories at one time of the day than at any other time of the day surprised us," says study director Kirsi-Marja Zitting. Together with her team at Brigham and Women's Hospital and Harvard Medical School in Boston, she explored the question of how our internal clock affects our metabolism, regardless of level of activity, sleep and eating habits.

For this they recruited seven volunteers who lived for about a month in a laboratory with no windows, clocks and access to phones or the Internet. The subjects were only allowed to sleep and eat when instructed by the researchers.



Biorhythm determines metabolism


The researchers "confused" the subject's organism by sending them to bed four hours later each night than the night before - for three weeks. "Because it was like traveling around the world every week, their biological clocks could not keep up," says study author Jeanne Duffy. Without external evidence of the actual time of day, her inner clocks had been forced to beat at her own pace. "That allowed us to determine the basal metabolic rate at all different 'biological' times of the day," says Duffy.

Among the so-called basal metabolic rate falls the energy that the body needs to maintain its functions - for example, for heartbeat, respiration and digestion. The basal metabolic rate is how many calories we burn when we rest and do not do any physical activity. As it turned out in the evaluation of the data, this value is not always the same, but differs from time of day to time of day.

Highest energy consumption in the late afternoon


The least was the energy consumption of the subjects in their "biological night" when their body temperature dropped. By contrast, in the late afternoon and early evening, the basal metabolic rate was highest - ten percent higher than in the early morning. "It could be that food increases us at times when our energy use is lower," says Duffy. The scientists therefore advise to schedule regular mealtimes - and ideally a main meal should fall into the window of maximum calorie consumption.

The conclusion of the researchers: Our biorhythm has a greater impact on our metabolism than previously thought. If he gets out of step, it can also affect the weight. For example, this could explain why people in shift work are on average more likely to be overweight.

"How much energy we burn or store as fat is influenced not only by what we eat, but also by when we eat and rest," says Duffy. "A regularity in our eating and sleeping habits is very important for the entire health."


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