A study carried out in a small group of female students has shown that mental exercise increases food intake. In a ‘within-subjects’ study, each student spent 45 minutes resting, reading a document and writing a summary, or performing a battery of computerised tests. At the end of each 45 minute period, the students were invited to eat as much as they wanted from a buffet.
When the students had been involved in mental activity, they consumed 200 – 250 kilocalories more than when they had been resting. No specific dietary preferences or differences in appetite sensation markers were seen after mental exercise compared with resting. Mean cortisol levels were significantly higher and there was a significant increase in variations in plasma glucose and insulin levels after mental activity. Since the period of mental activity used almost no extra calories compared with resting, this study suggests a new risk factor for positive energy balance with the potential to lead to obesity.