Past research found eating sugar could improve self-control. Now research suggests this effect only holds true if people think willpower is a limited and easily depleted resource. For those who believe willpower is plentiful, sugar had no benefits, findings detailed this week in the Proceedings of the National Academy of Sciences.
Recent research has suggested that sugar can improve mental functions such as memory and attention. These sugar boosts could apparently enhance self-control as well, improving things such as persistence and inhibition of impulses. It was typically assumed this was due to some effect sugar had directly on the brain
“The dominant theory of willpower says that we need constant fueling from glucose to maintain our willpower. It says that willpower is very limited, and it depends on a constant supply of glucose,” said psychologist Carol Dweck at Stanford University.
Still, a number of researchers questioned whether something as important as mental performance was so fragile as to depend significantly on short term boosts from sugar.
“It didn’t make sense that humans would be built to depend on sugar boosts every time we did something hard for 10 minutes,” Dweck said.
Dweck, along with Veronika Job at the University of Zurich and their colleagues, analyzed the effects sugar had on volunteers in conjunction with their beliefs about the nature of willpower. Some people thought willpower is limited and easily depleted — for instance, they believed that after strenuous mental activity, their energy was depleted and they had to rest to get it refueled. Others thought willpower is not easily used up — for example, they believed that after strenuous mental activity, they felt energized for even more challenges.
Scientists had 87 volunteers fill out questionnaires regarding willpower, drink lemonade sweetened with either sugar or an artificial sweetener, and complete a demanding task requiring they cross out some “e’s” in a text but not others. The participants next had to identify the color of words on a video screen as quickly as possible, which demands self-control when the combination of word and color is mismatched — for instance, the word “green” is written in red.
As expected, volunteers who believed willpower was a limited resource did more poorly in the self-control task if they drank the drink that lacked sugar. In contrast, people who believed willpower was not a limited resource performed with high levels of self-control with or without sugar boosts.
The researchers suggest the effects sugar can have might be due to how they stimulate the mouth or digestive system, triggering pathways connected to brain regions linked with responses to rewards. Such activity in turn can interact with preexisting beliefs regarding willpower — for instance, signaling the availability of energy, serving as motivation for sustained effort on challenging tasks for those who need it.
“Based on these results, we’re very interested in seeing if we can train willpower — whether we can teach people that their willpower is potentially abundant and how to use it effectively,” Dweck said.