Want to Play It Safe? Have a Cheeseburger

Sometimes it seems that everyone has abandoned the notion that rational self-interest drives people’s decisions. It’s high time for some answers to the next obvious question: If Reason doesn’t rule the mental roost, then what does govern people’s approach to buying, selling, voting, marrying, hiring and other choices? Last month, this study suggested that part of the answer is, simply, food. People who are hungry, it found, make different financial decisions than people who’ve recently eaten.

Mkael Symmonds, Julian J. Emmanuel and their colleagues had 19 men play a virtual lottery 200 times, each time picking between two choices on a computer screen. As in real life, their chances of winning, say, £20 were much better than their chances of winning £100. Each man played the game once a week for three weeks. Once, he had a nice meal first, and then played right away; another time, he ate and then waited an hour before hitting the computer; and, in the third time, he had to fast for 14 hours before playing.

If they were purely rational economic men, the volunteers invariably would have chosen the low-paying bets with the best odds of winning. And if they were ruled by their innate personality differences, they would have divided into risk-takers who consistently go for long shots and risk-avoiders who played it safe.

That’s not what happened.

When hungry, the men went for long-shots more often. This is consistent with work on animals. Hunger drives any creature to take risks it wouldn’t if it felt comfortable. And folk wisdom knows this too, of course: The personnel philosophy of Shakespeare’s Julius Caesar, for instance—“let me have men about me that are fat”—prompts him to mistrust “lean and hungry” Cassius(good call, as Cassius is engaged in the high-risk venture of plotting to kill him).

On the other hand, when they played one hour after eating, the men preferred lower-risk bets. In fact, their attitude toward risk rose and fell with their levels of the hormone acyl-ghrelin, a hunger signal that rises when the body wants food and falls after eating.

Even more interesting were the games played right after the meal, before acyl-ghrelin levels had time to change. In that situation, men with lower Body Mass Index scores (roughly, those whose look tends toward the “lean and hungry”) didn’t change their attitude toward risk, the authors write. But chubbier men took more risks right after they’d eaten. Symmonds et al. think this might have implications for the fight against obesity: Once a certain level of body fat is reached, they suggest, that act of eating itself might enable impulsive, high-risk choices. Like having another Twinkie. Or buying that lottery ticket.

Symmonds, M., Emmanuel, J., Drew, M., Batterham, R., & Dolan, R. (2010). Metabolic State Alters Economic Decision Making under Risk in Humans PLoS ONE, 5 (6) DOI: 10.1371/journal.pone.0011090