A U.S. researcher says willpower to keep from eating too much is stymied by larger packaging, cheap prices and big portions.David Levitsky, professor of nutritional sciences and of psychology at Cornell University, and co-author Carly Pacanowski, a graduate student, said their review article found powerful environmental cues are subconsciously bending willpower every day.\"We\'re slaves to our environment,\" Levitsky said in a statement. \"And it\'s not just the amount you put on your plate, but also the package size from which the food comes determines how much you will eat.\"Levitsky and Pacanowski analyzed hundreds of articles on eating behavior and found forces that individuals have no control over are heavily influencing the obesity epidemic in the United States.The review, published in the journal Public Health Nutrition, found these forces include cheap food prices and ease of access to unhealthy food.In addition, social factors such as seeing others eat are also strong stimulants, Levitsky said, and have taken on more strength in the past 50 to 60 years, as restaurant dining becomes more frequent.The review article also found portion size emerged as one of the most powerful links to overeating, the study said.