Researchers reporting in Current Biology on November 8 have made the surprising discovery that the number of calories people burn while at rest changes with the time of day. When at rest, people burn 10 percent more calories in the late afternoon and early evening than in the early morning hours.
The findings reinforce the important role of the circadian clock in governing metabolism. They also help to explain why irregularities in eating and sleeping schedules due to shift work or other factors may make people more likely to gain weight.
“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,” says Kirsi-Marja Zitting of the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital and Harvard Medical School, lead author of the paper.