Study co-authors Christine Logel of Renison University College at the University of Waterloo in Ontario and Geoffrey L. Cohen of Stanford University in California recruited 45 female undergraduates who had a body mass index of 23 or higher -- 58 percent of the women were overweight or obese.
Each woman was weighed, and then asked to rank values -- creativity, politics, music, and relationships with friends and family. Half were told to write for 15 minutes about the value that was most important to her.
The other half -- the control group -- were told to write about why a value far down on their list might be important to someone else. The women were weighed one month and four months later.
The study, published in the journal Psychological Science, found women who had written about an important value lost an average of 3.41 pounds, while women in the control group gained an average of 2.76 pounds.
"How we feel about ourselves can have a big effect," Logel said in a statement. "We think it sort of kicks off a recursive process. Maybe when one of the women who wrote about an important value went home that night, she felt good about herself and didn't eat to make herself feel better. Over a few months, that could make a real difference in her life."