I’ve just come back from the annual meeting of the Society for Judgment and Decision Making. One of the most interesting talks, by Roy Baumeister, demonstrated the power of lemonade to reduce decision biases.

Baumeister reported the results of a study published earlier this year in the journal Psychological Science by Masicampo and Baumeister (19:3, pp. 255-260). To understand the motivation for the study, think about the dual-process model of decision making discussed in Medical Decision Making: A physician’s guide. We have two parallel decision systems in the brain: one intuitive and heuristic, and one analytical. The intuitive system is fast and easy, but doesn’t always get it right. The analytical system can work out the right answer, but is slower and more effortful to use. Many biases in decision making are products of the intuitive system’s heuristics, particularly in situations when the analytical system doesn’t have the opportunity to correct our intution.

Masicampo and Baumeister point out that what “effortful” means, biologically, is that analytical thinking requires and consumes more energy in the brain. Energy is provided by glucose, transported through the blood. Thus we would expect that reducing or increasing glucose might impair or enhance the brain’s capability to use the analytical system, and thus impact susceptibility to decision bias.

In the study, 120 undergraduates drank lemonade, either sweetened with sugar (which increases blood glucose a few minutes later) or with Splenda (which does affect blood glucose.) Neither the participants nor the experimenters knew which drink they were given. In addition, half the participants performed a self-control task designed to deplete their resources (the other half did a similar task that did not require self-control). Finally, all the participants made choices that are susceptible to a decision bias called the attraction effect (described in the postscript below).

Those who drank Splenda-sweetened lemonade displayed the attraction effect more strongly than the other groups. Among the depleted group, in particular, sugar drinkers outperformed Splenda drinkers and performed as well as sugar drinkers in the non-depleted group (the best-performing group).

That is, a glass of (real) lemonade a few minutes before this decision task led to better decisions, apparently by restoring depleted cognitive resources.

Yet another reason to suggest that patients — and on-call residents — should eat well to improve decision making. (And yes, Baumeister appreciates the irony of trying to apply this finding to self-control decisions around dieting or diabetic glucose control).

Postscript: The attraction effect occurs when people make choices between options which involve trade-offs (for example, one washing machine is large and low-efficiency and the other is small and high-efficiency). Imagine that people are split 50/50 on which machine they prefer. To get the attraction effect, you add a third option (the “decoy”), which is strictly worse than one of the others (for example, a medium-sized low-efficiency washing machine would be strictly worse than the first washer). No one should ever choose the decoy, and no one does, but the addition of the decoy can have a dramatic and systematic effect on the choice between the two original washers. Now people are more likely to prefer the washer that’s better than the decoy (the first one, in our example) over the other washer; instead of a 50/50 split, 80% of of people might prefer the large low-efficiency washer. If you’re in the washing machine business and some reason to want to sell more large low-efficiency washers, this has obvious applicability. This effect is also sometimes called “asymmetric dominance”.