LEXINGTON, Ky. (Dec. 7, 2010) - The concept of the mind as an energy system is as old as Aristotle.
And an energy system needs fuel, like anything else. The fact that any type of exercise, mental or physical, will deplete one's energy reserves is a simple concept, but also one that has yielded quite a response from the scientific community to the research of University of Kentucky psychology professor Nathan DeWall.
"Energy is core to everything that we do," said DeWall. "If my computer wasn't plugged in, I wouldn’t expect to be able to use it. If I didn't pay my electric bill, I wouldn't be able to read before going to bed at night."
DeWall along with graduate assistant Timothy Deckman, Brad Bushman of The Ohio State University and Matthew Gailllot of SUNY-Albany, have taken the ideas of energy, self control and aggression even further in a study published in this month's Aggressive Behavior.
DeWall and his colleagues found that people who drank a glass of lemonade sweetened with sugar acted less aggressively toward a stranger than people who consumed lemonade with a sugar substitute.
Researchers believe it all has to do with the glucose, a simple sugar found in the bloodstream that provides energy for the brain.
"If you mentally exhaust people and then you offend them or make them angry, they are more aggressive," said DeWall. "Avoiding aggressive impulses takes self control, and self control takes a lot of energy."
The results are more than just a medical rarity, as the group did several studies showing that people who have trouble metabolizing, or utilizing glucose in their bodies display more evidence of aggression and less willingness to forgive others.
"Energy is key to positive emotions," said DeWall. "People are less impulsive and make better monetary choices with increased energy as well."
In the experiment, 62 college students fasted for three hours to reduce glucose volatility. They were told they were going to participate in a taste-test study, and then have their reaction times evaluated in a computerized test against an opponent.
Half of the participants were given lemonade sweetened with sugar, while the others were given lemonade with a sugar substitute.
After waiting eight minutes to allow the glucose to be absorbed in their bloodstream, the participants took part in the reaction test.
The reaction test has been used and verified in other studies as a way to measure aggression. Participants were told they and an unseen partner would press a button as fast as possible in 25 trials, and whoever was slower would receive a blast of white noise through their headphones.
At the beginning of each trial, participants set the level of noise their partner would receive if they were slower. The noise was rated on a scale of 1 to 10 -- from 60 decibels to 105 decibels, which is about the same volume as a smoke alarm.
Aggression was measured by the noise intensity participants chose on the first trial -- before they were provoked by their partner.
Results showed that participants who drank the lemonade sweetened with sugar behaved less aggressively than those who drank lemonade with a sugar substitute. Those who drank the sugar-sweetened beverage chose a noise level averaging 4.8 out of 10, while those with the sugar substitute averaged 6.06.
"Any type of exercise, mental or physical, will deplete your energy reserves, and people don't always pay attention to that," said DeWall, who first met Bushman as a graduate student at Florida State University. "People are more likely to lash out in exhaustion."
But this is only part of the story. "We've also found that people with difficulties metabolizing glucose have more aggressive personalities, are more vengeful and have problems with forgiveness," said DeWall.
In two other studies in the same paper, the researchers showed how problems metabolizing glucose may translate to problems on a societal level. Using 2001 data, the researchers found that the diabetes rates for each of the 50 states were linked to violent crime rates. Those states with higher diabetes rates also tended to have higher rates of murder, assault, rape and robbery, even after controlling for poverty rates in each state.
In a separate analysis, the researchers tested whether another medical problem related to glucose metabolism was linked to violence worldwide.
They examined the prevalence, in the populations of 122 countries around the world, of a deficiency in an enzyme called glucose-6-phosphate dehydrogenase. This enzyme is related to glucose metabolism. It is the most common enzyme deficiency in the world, afflicting more than 400 million people.
Countries with higher levels of the disorder also had more violent killings, even outside of war.
"We've gathered a lot of different pieces of evidence here--individual, state and global," said DeWall. "If you want to understand aggression, you have to take energy into account."
The findings were further supported in another series of studies, published recently in the journal Personality and Individual Differences.
In that paper, DeWall, along with Bushman and UK graduate student Richard Pond, had participants complete a commonly used and well-accepted checklist that measures the number and severity of Type 2 diabetes symptoms, such as numbness in the feet, shortness of breath at night, and overall sense of fatigue. In three separate studies, the same participants completed different measures of their willingness to forgive others.
On all three measures, people with higher levels of diabetic symptoms were less likely to forgive others for their transgressions. From 1980 through 2008, the number of Americans with diabetes has more than tripled (from 5.6 million to 18.1 million).
For many experiments, DeWall and his colleagues use sucrose, because of its fast action. "We want an immediate response to measure," he said. "But we're not advocating boxes of (candy) here."
DeWall recommends a balanced diet with lots of fruit and foods rich in protein that release glucose in a more consistent manner, which helps in avoiding dramatic glucose drops.
DeWall's research is about knowledge and awareness, as opposed to direction and prescription.
"Be aware of what you're doing to tax yourself throughout the day," he said. "Drama in the workplace, deficiencies in the coordination of efforts … all of this uses energy. Become aware of your limited energy and realize when you need to make changes."