Your body’s internal clock drives the ship of your day-to-day living. It tells you when you’re hungry, when you’re tired, and more.
That body clock also determines the time of day your body burns the most calories – even when you’re resting and doing nothing, a new study shows.
Researchers reporting in Current Biology found that when resting, we burn 10% more calories in the late afternoon and early evening than in the morning. So, don’t be so hard on yourself when you lazily succumb to an afternoon slump, your body will pick up the slack.
The study also reinforces the vital role our body clock plays in regulating metabolism, for example showing why those with irregular sleep schedules or working the late shift are more likely to gain weight.
To test the importance of our body clocks, the researchers studied seven participants for over a month in a laboratory that had no windows or clocks. They had no access to internet or phones, and were given schedules of when they could sleep, wake up, and eat.
Each night, the participants went to sleep four hours later than the night before, mirroring what one might experience as they travel around the world.
“Because they were doing the equivalent of circling the globe every week, their body’s internal clock could not keep up,” co-author Jeanne Duffy, of the division of sleep and circadian disorders at Brigham and Women’s Hospital in Boston, said in a statement. “This allowed us to measure metabolic rate at all different biological times of day.”
They found the participants burned the fewest calories late in the biological night, when people experience a drop in body temperature. Energy expenditure was highest about 12 hours later, in the biological afternoon and evening.
Going forward, the researchers say future studies will examine whether these changes in resting metabolic heart rate will contribute to weight gain in those who don’t keep regular sleep schedules. But until that research comes, stick to a normal, consistent schedule if you’re trying to lose weight (actually, it’s best for overall health, too).
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