The effect of sugar on performance seemed very real, but these researchers were suspicious of the way it worked. “Given the centrality of cognitive performance and self-regulation for human functioning and welfare in general,” their paper reads, “it would be striking if these functions were so fragile as to depend to a significant extent on the short-term ingestion of glucose.”

One theory the researchers had was based on previous research that indicated many people believe willpower was a limited resource. This belief could lead people to become dependent on glucose.

The idea is that when someone who thinks willpower is a limited resource starts to get hungry or their blood sugar drops, they freak out because they think their willpower is depleting. The belief that their willpower is depleting is what actually depletes their willpower and makes them perform worse on self-control tests.

Lemonade Psychology

In order to test the hypothesis, they whipped up a few batches of lemonade.

First, they quizzed their subjects about their attitudes towards willpower -- a six item inventory that asked them to evaluate statements like “After a strenuous mental activity, your energy is depleted and you must rest to get it refueled again” or “After a strenuous mental activity, you feel energized for further challenging activities.” Agreeing with the first statement was indicative of people who view willpower as a limited resource. Agreeing with the second was indicative of people who view willpower as a plentiful resource.

Then, they gave these subjects one of two kinds of lemonade, and then a common self-control test.

Half of the subjects were given lemonade made with sugar, the other half were given lemonade made with 0-calorie artificial sweetener. This is how you administer a placebo or “sugar pill,” when the substance being studied is itself sugar. (The researchers noted that “the subjects could not detect whether they had consumed a sugar or non sugar beverage.”)

People with a “plentiful willpower” attitude did well whether they were given sugar or not. People with a “limited willpower” attitude did much, much worse if they weren’t given sugar.

So really sugar is just a placebo. An addictive placebo.

If you THINK you'll have willpower, you will. Have. Power.