The results reinforce the important role of the circadian clock in the effectiveness of diets. According to a new study published in Current Biology, Brigham and Women’s Hospital and Harvard Medical School, late afternoon and evening are the times of day when we burn the most calories. Research shows that at rest people burn 10% more calories in the late afternoon and early evening than in the early morning hours. The results also help explain why irregularities in meals and sleep patterns due to shift work or other factors can make people more likely to gain weight. We talked about this with Dr. Elisabetta Macorsini, a nutritionist at Humanitas.

In the laboratory without a clock

To determine the changes over the course of the day in metabolism, the researchers studied seven people in a special laboratory without any clue as to what time he was out. There were no clocks, windows, telephones or the Internet. The study participants had assigned timetables for going to bed and waking up. Each night, times were set four hours later, the equivalent of a journey west through four time zones each day for three weeks.
“Because they were making the equivalent of a round-the-world trip every week, their body’s internal clock couldn’t keep up, so it was swinging at its own pace,” explained study co-author Jeanne Duff. This allowed us to measure the metabolic rate at all the different biological times of the day, understanding which were the times when people burned the most calories.

The importance of mealtimes

“The results we gathered reinforce the importance of the role played by the circadian clock, which is the 24-hour rhythm that regulates the alternation of sleep and wakefulness and governs the metabolism,” commented Dr. Macorsini. It also helps explain why irregularities in the patterns of meals and sleep due to work shifts or other reasons contribute to increase body weight.