I am getting older and keeping the pounds off is harder so this article struck home, especially as a Dad. Intellectual work leads to higher calorie intake. The following quote gives you most of the findings.
"The research team, supervised by Dr. Angelo Tremblay, measured the spontaneous food intake of 14 students after each of three tasks: relaxing in a sitting position, reading and summarizing a text, and completing a series of memory, attention, and vigilance tests on the computer. After 45 minutes at each activity, participants were invited to eat as much as they wanted from a buffet.
The researchers had already shown that each session of intellectual work requires only three calories more than the rest period. However, despite the low energy cost of mental work, the students spontaneously consumed 203 more calories after summarizing a text and 253 more calories after the computer tests. This represents a 23.6% and 29.4 % increase, respectively, compared with the rest period."
The article goes on to note that glucose and insulin levels vary more widely during intellectual work. A need for glucose, being the brain's fuel, may be a factor in this desire to eat after intellectual work.
We have noticed this in our kids for quite a while. After studying, they go straight for the fridge or the pantry. My son has a tendency to put on weight, so we have decided on a proactive course. We try to get homework done right before dinner when possible. When we cannot, we keep tabs on when he is finishing, and invite him to join us in an apple or pre-cut up orange just as he is done. He gets a healthier snack without us preaching at him and avoiding power struggles over the bad foods.
It is good to know that the next time your teen says he/she is famished after studying, science has shown they probably aren't entirely exaggerating,