This last breakthrough, published in 2007, came accidentally, in a tale of academic intrigue involving Mardi Gras and a “joyless drink of glop.” By one theory, Mardi Gras allows for people to indulge their sins before Lent, and Baumeister and his fellow researchers set out to test whether pleasure might increase self-control reserves by having subjects drink ice cream milkshakes between two tasks requiring willpower.
As a control, some subjects drank a “large, tasteless concoction of low-fat dairy glop.” But the researchers found, to their initial dismay, that both the ice cream shakes and the joyless glop reversed the effects of depletion. It wasn’t pleasure that rejuvenated willpower, it was the calories, a discovery they confirmed by measuring glucose levels after self-control tasks, and, also, by comparing the effects of lemonade with sugar versus lemonade with Splenda.
This finding, as the authors detail, has impressive explanatory power. In one real-world study published earlier this year, researchers found that Israeli judges making parole decisions were likely to grant parole roughly 65 percent of the time after a meal break, but approved parole almost never right before one. Weighing parole decisions appears to consume glucose.
Some 90 percent of juvenile delinquents tested soon after being taken into custody, another study found, had below-average glucose levels. Yet another study, this one in Finland, revealed that just by looking at the glucose tolerance of convicts about to be released, researchers could predict future violent crimes with roughly 80 percent accuracy. The glucose-willpower link also sheds light on self-control problems in diabetics, hyperglycemics, and even women at that energy-scarce time of the month.
This agrees with another finding that IQ depends on energy level. Interesting to see the neural science part of willpower and self control.