A new study in the journal Preventive Medicine looked at the data from Behavioral Risk Factor Surveillance System, a survey of that asks nearly 400,000 Americans to self-report their weight in 2008 and 2009. Researchers then compared these self-reports to obesity data reported by American doctors: hard data, the actual numbers on the scale. According to the self-reports, the rate of obesity decreased between 2008 and 2009. But the truth is that obesity rates increased, for both men and women, in that time.
The conclusion? A great majority of Americans are deceiving themselves when it comes to weight gain, and it turns out that self-deception is a fairly common phenomenon.
Professor Robert Trivers has spent his career studying the evolutionary psychology behind self-deception. He describes this phenomenon in his book, "The Folly of Fools: The Logic of Deceit and Self-Deception in Human Life."