"Often the fat-free version is not much lower in calories than the regular version. For example, each low-fat Oreo cookie has 50 calories. The regular version has just over three calories more". - Brian Wansink (Author)

More on his Amazon Blog

During a recent experiment, a French colleague, Pierre Chandon, and I invited people to watch some commercials and a video episode of the 'Dukes of Hazzard.' We gave them bags of granola that were labeled as either 'Low-fat Rocky Mountain Granola' or 'Regular Rocky Mountain Granola,' as we described in the current issue of Journal of Marketing Research. In reality, all of the granola was low fat. While people watched the video, they ate the granola. Those given what was labeled as low-fat granola kept munching long after the other group stopped. After the movie, we weighed the remaining granola to see how much had disappeared. It turned out that those eating what they thought was low-fat granola ate 35 percent more, which translated into 192 more calories. When we offered them low-fat chocolate, they loaded up on 23 percent more calories.

More: Brian Wansink in the New York Times