Policies that mandate calorie labeling in fast-food and chain restaurants have had little or no observable impact on calorie consumption to date. In three field experiments, we tested an alternative approach: activating consumers’ self-control by having servers ask customers if they wanted to downsize portions of three starchy side dishes at a Chinese fast-food restaurant. We consistently found that 14–33 percent of customers accepted the downsizing offer, and they did so whether or not they were given a nominal twenty-five-cent discount. Overall, those who accepted smaller portions did not compensate by ordering more calories in their entrées, and the total calories served to them were, on average, reduced by more than 200. We also found that accepting the downsizing offer did not change the amount of uneaten food left at the end of the meal, so the calorie savings during purchasing translated into calorie savings during consumption. Labeling the calorie content of food during one of the experiments had no measurable impact on ordering behavior. If anything, the downsizing offer was less effective in changing customers’ ordering patterns with the calorie labeling present. These findings highlight the potential importance of portion-control interventions that specifically activate consumers’ self-control.