Researchers from Purdue University in Indiana performed experiments on lab rats. Researcher Susan Swithers said, "Substituting a part of the diet with a similar tasting item that has fewer calories sounds like a commonsense approach to lose weight, but there are other psychological functions at work.
"Tastes normally alert the body to expect calories.When those calories aren't present, we believe the systems become confused and one of the body's mechanisms to control food intake can become ineffective."
So when eating diet foods, the chances are the body will tell you you are still hungry and you will consume more calories and so gain weight.
From the December 5, 2011, Prepared Foods' Daily News.