Differential effects of fructose and glucose preloads on carbohydrate metabolism and later food intake were examined in both lean and obese subjects. In study 1, a preload of either 50 g of fructose or glucose was administered in solution, and food intake at a buffet lunch presented 2.25 h after preload was assessed. Significant differences in caloric intake were observed between load conditions with the fructose group consuming fewer calories than the glucose group. Obese subjects demonstrated significantly greater insulin responses to the preload compared with lean subjects, and insulin levels of obese subjects at 15, 30, and 45 min after preload were found to correlate significantly with amount consumed. Incorporation of fructose or glucose into a mixed meal format in study 2 revealed no differences in subsequent caloric intake as a function of either type of preload or percent overweight. Differing insulin levels are discussed as a possible mechanism for differential food intake.