It may sound like a good idea to contemplate an important decision over a meal, but a recent study has shown that eating food is not something you want to be doing when you have a quandary to solve and that going in hungry will keep you mind clear... despite what your stomach may be angrily grumbling at you.
The paper, "Always Gamble on an Empty Stomach: Hunger Is Associated with Advantageous Decision Making", published on PLOS ONE late last month, describes a series of three "experimental studies" that resulted in subjects who abstained from breakfast performing better on the Iowa Gambling Task than those who did not.
The task itself involves selecting cards from a series of decks, with some cards providing rewards and others penalties. The decks are not equal, with some delivering worse results than others. If your decision-making skills are up to scratch, you'll be better at identifying the poorer decks and sticking to the good ones.
Apart from water, participants in the studies had to not eat or drink anything starting from the evening before. Once they turned up for testing, between 8:30-9:15am, some would be randomly provided breakfast, leaving others hungry. It's important to note that those who did eat were told they could have "as much [as] they wanted".
Eating too much of certain foods (but not necessarily turkey, as Mythbusters once showed) can definitely have an affect on your alertness. I have to wonder if the subjects, given a free meal, took the opportunity to load up. Given those tested were university students and the types of food provided are not detailed -- other than 200mL of yoghurt to "assure a minimal level of satiation" -- it's not outside the realms of possibility.
So the takeaway then is not to make important decisions in situations where your mental faculties might be comprised, such as when you're tired.