Here's a interesting study.
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.
Students who chose the cake reported a stronger emotional decision making drive while those who chose the fruit salad reporter a stronger cognitive drive.
Researchers hypothesized that the difference was explicable on the basis of the 7 digit memory group having "lower levels of processing resources" with much of their cognitive brain power being spent on trying to remember their 7 digit number.
Moral of the story?
Don't eat on a full brain.
Shiv, B., & Fedorikhin, A. (1999). Heart and Mind in Conflict: the Interplay of Affect and Cognition in Consumer Decision Making Journal of Consumer Research, 26 (3), 278-292 DOI: 10.1086/209563