Six out of 10 Americans are overweight or obese, and obesity among American adults has nearly doubled since 1980. CNN Medical Correspondent Elizabeth Cohen examines the issue and finds that losing weight isn't the problem for many people. The problem lies in not regaining the lost weight. Cohen talks to two people who were successful in losing weight and keeping it off, and reports on research that suggests genetics may play a role in predisposing people to be overweight.