People who use their brains to complete tasks eat more than those who just relax, according to a study at Universite Laval in Quebec.

Researchers had 14 students try one of three activities: sitting and relaxing; reading and summarizing a text; or completing memory and other tests on a computer.

After 45 minutes, they were offered a buffet.

Students who did the reading ate 203 more calories than those who rested. Those who did the computer work ate 253 more calories. But, researchers said, they had already found that the computer work only used three more calories.

Blood samples also showed that intellectual work causes much bigger fluctuations in glucose and insulin levels.

"These fluctuations may be caused by the stress of intellectual work, or also reflect a biological adaptation during glucose combustion," said lead author Jean-Philippe Chaput.

He also said that the overcompensation could be part of the obesity epidemic around the world.