Thinking too much can make you eat more. Researchers at Universite Laval say intellectual work raises peoples' calorie intake and could be a reason for obesity.

A group of 14 students were invited to eat as much as they wanted at a buffet, after taking part in three different tasks:

• Sitting down and relaxing
• Reading and summarizing a text
• Finishing memory and attention tests on a computer

All the tasks turned out to be low energy -- students only needed three more calories to do the mental work than to rest. However, they spontaneously ate 203 more calories after summarizing the text and 253 more calories after the computer tests.

Blood samples taken before, during, and after the sessions also showed that there were more pronounced changes in glucose and insulin levels during mental work than when resting.

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

The brain uses glucose as fuel and the body could be trying to keep its glucose balance in check, by taking in more food, he said.

"Caloric overcompensation following intellectual work, combined with the fact that we are less physically active when doing intellectual tasks, could contribute to the obesity epidemic currently observed in industrialized countries," Chaput said. "This is a factor that should not be ignored, considering that more and more people hold jobs of an intellectual nature."