By Tia Ghose, Staff Writer
Published: 08/19/2013 03:17 PM EDT on LiveScience
Willpower may be plentiful -- as long as you believe it is.
People who consider willpower a finite resource tend to need a sugar pick-me-up to continue working on a hard task, whereas those who believe willpower is abundant don't, new research suggests. Moreover, nudging people's beliefs about willpower in one direction or the other can influence how they behave.
The findings, published today (Aug. 19) in the journal Proceedings of the National Academy of Sciences, contradict earlier studies that suggested that willpower is quickly depleted.
In recent years, a growing body of research suggested that willpower is like a muscle that tires out if used too much. Other studies hinted that a physical boost could replenish that flagging resource. For instance, participants in one study who drank a sugary drink could maintain self-control after a mentally challenging task. [10 Things You Didn't Know About You]
The idea was that willpower takes energy and, therefore, depletes the brain's glucose supply. As a result, a sugar rush would replenish people's willpower by refueling the brain, earlier studies suggested.
But people run ultramarathons, participate in Ironman competitions or do hours of backbreaking work without needing to gorge on food the entire time. And simply swishing a sugary drink without actually consuming it can have the same energizing effect in athletes.
"We have ample glucose supply in our bodies," said study co-author Carol Dweck, a psychologist at Stanford University.
Need a boost?
Dweck and her colleagues asked 87 college students in Germany, Switzerland and the United States to describe their beliefs about willpower. Some subscribed to the willpower-as-muscle idea, whereas others believed willpower was plentiful and even grows the more it's used.
They then asked the study subjects to complete a mentally challenging task such as crossing out certain letters in a passage using complicated rules, followed by a second task that required participants to resist an impulse, such as reading the name of a color written in the wrong color ink (the word "green" written in red, for instance).
Those who believed willpower was limited tired after the first task and performed poorly on the second. If they received a sugary drink that took effect after the first task, however, their second performance improved.
Those who believed willpower was abundant didn't tire during the second task, and got no boost from the sugar.
Power of belief
But it wasn't clear that the beliefs about willpower altered performance: After all, people who believe willpower is limited may simply assess their own abilities accurately and realize they will tire out easily.
To rule out that possibility, the team gave a second group of people a survey meant to nudge them toward believing that willpower was either finite or abundant.
Those nudged to believe that willpower was finite tended to need the sugary drink to perform well, whereas those nudged in the opposite direction didn't need the pick-me-up.
The results suggest that physiologically, willpower shouldn't be depleted; rather, people's beliefs may be shaping their behavior, Dweck said.
"We believe that people who believe willpower is limited are always looking for cues about their resources -- 'Am I tired? Am I hungry? Do I need a boost?' -- and feel that they can't work unless they're constantly replenished," Dweck told LiveScience.
Past studies may have shown that willpower can be depleted because most people in society tend to believe willpower is a limited resource, Dweck added.
As a follow-up, the team is doing experiments to reorient preschoolers' beliefs about willpower.
"We teach them about willpower -- that it is a self-generating thing, that the longer you wait and the harder you try, the more you can. And it seems to be effective," Dweck said.