Opt-IN is a 6-month behavioral telephone-based weight loss program that encourages participants to follow a low-calorie, low-fat diet. Participants are also encouraged to engage in a moderate level of physical activity, such as brisk walking. Behavioral coaching will be delivered remotely via telephone calls throughout the 6-month study, and participants will be randomized to receive a combination of components designed to aid in weight loss. Participants must own an iPhone, and will download a weight loss application onto their smartphone in order to track food intake and physical activity throughout the study. If youre interested in participating, please visit our website