It seems that if you eat on a full brain you are more likely to make poor eating decisions.
So here's the schtick via Weighty Matters:
Simple experimental design. Take 165 undergraduate students and enroll them in a study you tell them is about memory and where as part of their reward for inclusion, they'll be given a snack. Ask half of them to memorize a 2 digit number and the other half a 7 digit number and once they've memorized their numbers ask them to go into a second room where they are faced with their snack choice - either a piece of chocolate cake or a cup of fruit salad. Track choice and then follow up with an exploration of the students' perceived reasons for making the choice.
"63% of the students who were trying to remember the 7 digit number chose the cake compared with only 42% of those trying to remember the 2 digit number."
I totally buy the results, since I really did gain weight during my dissertation from a combination of sweet pastries for breakfast, sandwiches involving bacon and ranch dressing, huge portions at dinner (I like cooking so we go a bit overboard cooking crazy stuff), and of course a liberal helping of these (and yes I had the Camo cans):
The explanation put forth (which I don't entirely believe) to explain these findings is that the group that memorized the 7 digit number had "lower levels of processing resources" so that they weren't able to effectively use cognitive reasoning to choose the healthier option.
I think a more likely explanation is that the meta knowledge (or even without the conscious realization) that you are at your limit for cognitive resources stresses the shit out of you. I'll bet if you gave someone two lists of 4 items (well below that upper short term memory limit), one with stressful words and one with nice words you would get a similar effect. Anyway... cool result.
HT: Dan Simons
I always thought it was related to glucose levels in the brain. The brain burns glucose when you do heavy mental lifting. Mental activity can lead to low brain glucose, which triggers hunger, fatigue, and carbohydrate cravings, even though the rest of your body still has plenty of glucose to work with.
This is why I eat at least one piece of cake for every seven numbers I remember.
That's my story, and I'm sticking to it.
I think HP's glucose explanation is probably the most likely one, but I'll also put forward another explanation:
If you're working hard (with your brain or otherwise), you may feel like you deserved the tastier (unhealthier) snack as a reward for your hard work. The fact that it's less healthy may be inhibited by the idea that it is more okay to do something bad (taking the unhealthy snack) after/during doing something good (working hard).
Another explanation which is more in line with the one from the article is that people under stress might feel like they have enough to worry about right now and that worrying about how healthy their food is, is not something they want to add to the stress pile right now.