This is the point in the day when you burn the most calories
New research published in Current Biology has found that the amount of calories your body burns over the course of the day can vary.
A small study conducted by scientists at Brigham and Women's Hospital and Harvard Medical School found that when at rest, people naturally burn around 10 per cent more calories in the late afternoon and early evening than in the early hours of the morning, further supporting the link between metabolism and circadian rhythms – or body clock – that tells us when to sleep, wake and eat.
Lead author Kirsi-Marja Zitting from the division of Sleep and Circadian Disorders at Brigham and Women's Hospital and Harvard Medical School said: "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."
The researchers say the findings help to explain why disruptions to sleeping and eating patterns can make people more likely to gain weight, something often experienced by people who work night shifts.
In a 37-day experiment, they studied a group of seven participants, so we should emphasis that this study really is tiny, in a special lab that had no clocks, windows, phones, or internet so that they'd have no concept of time. They were told when to go to bed and wake up, and each night those times were adjusted four hours later – that's equivalent to travelling westward across four time zones each day for several weeks.
The results showed that resting energy expenditure is lowest late at night and highest about 12 hours later, in the afternoon into evening.
"Because they were doing the equivalent of circling the globe every week, their body's internal clock could not keep up, and so it oscillated at its own pace," co-author Jeanne Duffy, of the same division, explains. "This allowed us to measure metabolic rate at all different biological times of day."
When it comes to burning calories, it's not just about what we eat, but when Duffy concludes, adding: "Regularity of habits such as eating and sleeping is very important to overall health."
Duffy told Time that the increase in calorie burning is equivalent to around 130 extra calories. But before you start planning all of your workouts and mealtimes for the late afternoon, she highlights that the study only looked at the change in metabolic rate while people were at rest, however she did suggest that you might want to avoid eating during the window when calorie-burning is at it's lowest.
"Let’s say we get up an hour or two hours early and eat breakfast an hour or two hours early," she told the magazine. "We may be eating that breakfast not only at a time when our body might not be prepared to deal with it, but at a time when we need less energy to maintain our functions. Therefore, the same breakfast might result in extra stored calories, because we don’t need those to maintain our body functions."
Given the small sample, more research is needed before solid conclusions can be drawn from the study. The scientists' next project will look at how appetite and the body's response to food varies with the time of day.
