We burn more calories in the afternoon and evening, study finds

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(Megan Schmidt/ Discover) — Our weight might not be controlled solely by what we eat. When we eat, and when we get to sleep, may be just as important. A small study published this week in Current Biology found people who had been thrown off their circadian rhythms burn more calories in the late afternoon and evening hours than in the morning, when calorie burn is at its lowest. Later in the day, calorie burn increases by 10 percent, or about 129 calories.

To study how metabolism changed — independent from the effects of diet, exercise and the sleep-wake cycle — researchers kept the study’s seven participants in a lab isolated from outside influences. For 37 days, participants lived in windowless rooms without clocks, phones or the internet. Their food intake was carefully controlled and calorie-burning exercise was avoided. To throw off their internal clocks, assigned bedtimes each night were four hours later than the previous night — the equivalent of circling the globe and crossing all of its time zones over the course of a week.

“Their body’s internal clock could not keep up, and so it oscillated at its own pace,” said study author Jeanne Duffy, a neuroscientist in the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital. “This allowed us to measure metabolic rate at all different biological times of day.” (…)

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