It's not actually clear, however, that the brain is suffering some sort of glucose shortage in these moments. And several studies of athletes have found that simply tasting, but not consuming, a sweet energy drink can boost performance, even when the athletes have plenty of carbohydrates available to their muscles already.
Those findings prompted Hagger and his colleagues to find out whether it's glucose metabolism, or simply the taste of sugar, that revs up self-control. They conducted a series of five experiments in which participants completed willpower-depleting tasks, such as reading something boring or completing impossible word scramble puzzles. In one experiment, participants had to exert their willpower in a feat of physical strength, squeezing a hand grip. In another, they were asked to avoid the temptation of a plate of cookies and eat some radishes instead. In yet another, they were asked to drink as much as they could stand of a gross but supposedly healthy drink (actually a mixture of orange juice and vinegar).
Test of Willpower
After having their self-control tested with one task, the participants were given either a glucose drink or a drink containing no sugar but sweetened artificially. They were told to swish the beverage in their mouths but not swallow it. Finally, the researchers assigned a second tedious task to the participants, measuring how well they bucked up to meet the challenge.
In all cases, the participants who got the real-sugar mouthwash performed better than those who rinsed with the artificially sweetened drink, the researchers reported Sept. 20 in the journal Personality and Social Psychology Bulletin.
"So, practically, when people think that they are going to engage in a demanding task requiring self-control for a period of time (such as doing some boring filing, doing exercise, and resisting tempting foods when on a diet), they should introduce sugar into their mouths by some practical means," Hagger said.
Avoid Artificial Sweeteners
Just be careful that the beverage isn't sweetened with aspartame or some other artificial sweetener. Most likely, Hagger said, the mouth contains receptors that respond to real sugar by sending signals to the brain that activate regions associated with motivation and control. The same is not true for artificial sweeteners.
As to how much candy you'll need, researchers are still working on that.
"We also want to see how long-lasting these effects are," Hagger said. "That would give us an idea as to whether the glucose-tasting effect on self-control is long-term or relatively short-lived."