This Is the Time of Day When You Burn the Most Calories

Want maximum burn for your workout? Know your circadian rhythm.

Eating pizza

The intensity of your workout isn't the only thing that affects how many calories you burn. Studies have found that found that you burn more calories in cold temperatures thanks to a process called thermogenesis, and you also burn more calories in the sweltering heat thanks to a process called thermoregulation. But, seasonal changes aside, are there other factors that influence your burn? For instance, what about the time of the day?

It turns that that there is an optimal time in your daily schedule when your body is ready to burn, baby, burn.

According to a new study published in Current Biology, your "circadian system also modulates energy expenditure," which is a fancy way of asking if our body's internal clock (the one that lets us know we need to wake up in the morning and go to sleep at night) affects our digestion rates.

The study says we burn about 10 percent more calories in the afternoon and early evening than early in the morning or late at night. Specifically, we burn the least amount of calories at 5 am, and the most amount at 5 pm. So if you're looking to have a cheat meal, that's probably the best time to do it.

"The fact that doing the same thing at one time of day burned so many more calories than doing the same thing at a different time of day surprised us," Kirsi-Marja Zitting, a postdoctoral research fellow at the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital, and lead author of the study, said in a press release.

While the study was small, with only 7 participants, it was conducted in a laboratory setting, which makes the results more accurate than if they had been self-reported by a larger group. If they're accurate, the findings could shed light on why people who work night-shifts (and therefore eat at irregular hours) are at greater risk for obesity. It would also explain why drinking late into the night and feasting on several slices of pizza at five in the morning is a surefire way to gain weight.

The findings only bolster what many in the sleep field—and professional sports field—have known for a long time. According to Charles Czeisler, Ph.D., M.D., an expert at Harvard and one of the world's foremost sleep scientists, humans reach their maximum "wakefulness" in the late afternoon or early evening. That's when, he's explained, our ancestors would need to have spare reserves of energy to find food, build a fire, and prepare for dark. That late-day surge of wakeful hormones is still useful today in a world in which we don't forage for food. In athletic terms, it's also when, Czeisler noted, most Olympic records are broken.

So if you want to be healthy and maintain your ideal body weight, the best thing you can do for yourself is stick to a schedule in keeping with your internal clock.

"It is not only what we eat, but when we eat—and rest—that impacts how much energy we burn or store as fat," study co-author Jeanne Duffy said. "Regularity of habits such as eating and sleeping is very important to overall health." And for more tips on how to do just that, read about how I Tried Clean Sleeping for Two Weeks and It Changed My Life.

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Diana Bruk
Diana is a senior editor who writes about sex and relationships, modern dating trends, and health and wellness. Read more
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