People can exercise only so much self-control

USA Today
March 22, 2011

People who overtax their self-control may find they have less in reserve for later, suggests an intriguing new study that may have implications for people trying to lose weight or make other behavioral changes.

But lack of sleep does not appear to affect self-control, say the researchers, whose study of 58 subjects is in the March issue of the journal Social Psychological and Personality Science.

The subjects — half had stayed awake for 24 hours and half were well-rested — were shown scenes involving vomit and excrement from two movies, Monty Python's The Meaning of Life (1983) and Trainspotting (1996).

Some were allowed to express reactions; others were told to show no emotion. Later, they played an aggressive game in which they won or lost by chance. Winners were allowed to blast their opponent with a loud noise.

Those who had suppressed their emotions blasted their opponent at a noise level about 33% higher than those who were allowed to show emotion, regardless of how much sleep they'd had, researchers found.

Results suggest that "people have a diminishable supply of energy that the body and mind use to engage in self-control," says study author Kathleen Vohs, a consumer psychology professor at the University of Minnesota's Carlson School of Management. "When people use this energy toward achieving one goal, they have less of it available to use toward achieving other goals."

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