The primary goal of this clinical trial is to examine whether provision of portion-controlled prepackaged foods in the context of a reduced-energy diet prescription and counseling is associated with a greater degree of weight loss at three months in overweight or obese men and women, compared to usual care or control conditions in which the prescribed reduced-energy diet is to be consumed via self-selected foods. The effect on body weight and recognized indicators of disease risk, diet quality and cardiopulmonary fitness, as well as meal satiety and satisfaction, will also be examined. Participants are 184 overweight or obese men and women in San Diego area who will be randomly assigned to usual care or control conditions.