During the past 15-20 y, the incidence of overweight and obesity in the United States has grown rapidly. The processes that underlie this alarming trend remain largely unspecified. We hypothesize that degradation of the ability to use certain orosensory cues to predict the caloric consequences of intake may contribute to overeating and excessive weight gain. The results of two preliminary studies with rats are consistent with this hypothesis. In one study, the ability of rat pups to regulate their caloric intake after consuming a novel high-calorie, sweet food was disrupted if they had received prior training with sweet tastes that failed to predict the caloric consequences of eating. Another study found that altering the normal predictive relationship between food viscosity and calories led to increased body weight in adult rats. Dietary factors that degrade the relationship between sweet tastes, food viscosity and calories may contribute to overeating and weight gain.