Together with his former Case Western Reserve University colleagues Ellen Bratslavsky, Mark Muraven, and Dianne Tice, he examined the effect of a tempting food challenge designed to deplete participants' willpower through the awful power of an unfulfilled promise of chocolate!
In the first part of the trial, Baumeister kept the 67 study participants in a room that smelled of freshly baked chocolate cookies and then teased them further by showing them the actual treats alongside other chocolate-flavored confections. While some did get to indulge their sweet tooth, the subjects in the experimental condition, whose resolves were being tested, were asked to eat radishes instead. And they weren't happy about it. As the scientists noted in their Journal of Personality and Social Psychology paper two years later (PDF), many of the radish-eaters "exhibit[ed] clear interest in the chocolates, to the point of looking longingly at the chocolate display and in a few cases even picking up the cookies to sniff at them."
After the food bait-and-switch, Baumeister's team gave the participants a second, supposedly unrelated exercise, a persistence-testing puzzle. The effect of the manipulation was immediate and undeniable. Those who ate radishes made far fewer attempts and devoted less than half the time solving the puzzle compared to the chocolate-eating participants and a control group that only joined this latter phase of the study. In other words, those who had to resist the sweets and force themselves to eat pungent vegetables could no longer find the will to fully engage in another torturous task. They were already too tired.
In the psychology world, the key finding of this seemingly silly study was a breakthrough: self-control is a general strength that's used across different sorts of tasks -- and it could be depleted. This proved that self-regulation is not a skill to be mastered or a rote function that can be performed with little consequence. It's like using a muscle: After exercising it, it loses its strength, gets fatigued, and becomes ineffectual, at least in the short-term. Perhaps more importantly, this research would go on to serve as the foundation for at least 1,282 other studies involving everything from consumer to criminal behavior. It would, for instance, help show why people areenergized by positive messages, more likely to engage in retail therapy when brokenhearted, and better off tricking themselves into eating less than willfully dieting.