To Make Wiser Decisions, Eat or Drink First

It may be that life’s important decisions should come labeled “eat before you choose.” Researchers have discovered a link between the body’s level of blood sugar — essentially, the amount of energy you have at any given moment — and your ability to make wise decisions.

Decision Testing

A team of researchers at the University of South Dakota, led by psychology professor Xiao-Tian Wang, PhD, set out to explore what effect changing blood glucose levels had on decision-making. Sixty-five students were given a list of 14 questions asking them to choose between a pair of monetary rewards — a smaller reward that could be received sooner and a larger reward that the students would have to wait longer to get. One example was “Would you prefer to receive $120 tomorrow or $450 in 31 days?” To encourage thoughtful and honest responses, participants were told that they would have an opportunity to roll dice at the study’s conclusion for a chance to win one of their actual choices.
Dr. Wang first measured the blood glucose levels of the students, then asked them to answer seven questions. Next they were given a caffeine-free soda, sweetened either with sugar or with the artificial sweetener aspartame (they didn’t know which), and asked to drink it. Their blood glucose levels were then measured again. Ten minutes later, they were asked the remaining seven questions. Dr. Wang found…
  • Students who drank the sugary soda were more likely to choose a larger reward later than to go for the fast cash in lesser amounts. Speaking purely financially, this was the wiser decision because the amounts of the delayed payments were far higher than the payments they could receive immediately.
  • Students who drank artificially sweetened soda (which contains no calories and therefore doesn’t provide the body with energy) had the opposite response — they were more likely to choose the “smaller and sooner” monetary rewards.
Results were published in the February 2010 issue of Psychological Science. Dr. Wang’s coauthor was doctoral student Robert Dvorak.

How Sweet It Is

These results raise an interesting question: Why would a relative lack of energy in your body (in other words, being hungry as evidenced by the lower blood sugar levels) affect decisions you make about money? Dr. Wang offered his best guess — when we’re hungry, our bodies and minds experience a general feeling of need, which leads us to grab for every available resource, whether it’s food or something else. In such situations, patience (what’s required to willingly delay a reward now for a larger one to be received later) goes out the window.
Earlier theories set out by other researchers had argued that our society’s overwhelming focus on wealth is an outgrowth of our evolutionary desire for food… and that both are partially regulated by the amount of glucose in our bodies. Dr. Wang’s hypothesis is that these same evolutionary reasons might explain how caloric energy enables us to be more future-oriented in our decision-making. “The future is more abstract than the present and thus may require more energy to process,” he says. These ideas are interesting, but Dr. Wang cautions that this is basic research, and it’s a leap to arrive at real-world conclusions.

Future research may find applications for treatment of people with impulsive behaviors and disorders, such as addictions or anorexia. In the meantime, since this study demonstrated that even blood glucose fluctuations within a normal range — after drinking just one soda — affect decision making, I’ll make a point to avoid making big decisions on an empty stomach!