Diet foods have been around since the early 1960s. Since then, obesity rates have skyrocketed, even as food producers concoct new low-calorie or calorie-free products. A Purdue University study on rats found that animals fed a high-fat diet that also contained potato chips made from Olean, calorie-free fat substitute, gained more weight than rats fed the same diet with high-fat potato chips. It seems that the fat substitute interfered with the body’s capacity to regulate weight through hunger and metabolic rate.

Other studies have shown similar results with calorie-free soft drinks. People who drink more diet sodas tend to be fatter than people who don’t drink them. Interfering with the body’s ability to predict caloric content from taste appears to trigger obesity. (Behavioral Neuroscience, published online June 20, 2011)