If you like dessert, don't keep it at home. This is obvious, but it's also one of the most effective options (you can't eat something you don't have). If you really want it, make yourself do a little work. Have dinner, and if you have a craving for dessert afterwards then go out and get some. Chances are it won't take more than 20 minutes for that craving to die, as you'll fill up and won't want to eat anything else. In the event it doesn't, go out and buy a reasonably-sized dessert. As long as you're not inclined to do this regularly, prolonging the decision to eat dessert should help you out.
A small but revealing study suggests that even mildly stressful intellectual challenges change our emotional states and behaviors, even if they do not profoundly alter brain metabolism. Fourteen female Canadian college students either sat around, summarized a passage of text or completed a series of computerized attention and memory tests for 45 minutes before feasting on a buffet lunch. Students who exercised their brains helped themselves to around 200 more calories than students who relaxed. Their blood glucose levels also fluctuated more than those of students who just sat there, but not in any consistent way. Levels of the stress hormone cortisol, however, were significantly higher in students whose brains were busy, as were their heart rates, blood pressure and self-reported anxiety. In all likelihood, these students did not eat more because their haggard brains desperately needed more fuel; rather, they were stress eating.
Messier has related explanation for everyday mental weariness: "My general hypothesis is that the brain is a lazy bum," he says. "The brain has a hard time staying focused on just one thing for too long. It's possible that sustained concentration creates some changes in the brain that promote avoidance of that state. It could be like a timer that says, 'Okay you're done now.' Maybe the brain just doesn't like to work so hard for so long."