The United States is the epicenter of an obesity pandemic. As more countries acculturate to a Western lifestyle, rates of obesity and its sequelae are rising steadily in both adults and children. In response, a variety of weight-loss diets emphasizing alternative distributions of macronutrient classes have been promoted with considerable success. Among the most popular is the so-called "Atkins Diet," in which carbohydrate restriction is touted as the key to weight loss. Despite claims, however, evidence that weight loss is enhanced by means other than caloric restriction is lacking. Also lacking is evidence that fad diets produce sustainable weight loss. Most important, fad diets generally ignore or refute what is known about fundamental associations between dietary pattern and human health. Cancer, cholera, and AIDS induce rapid weight loss, highlighting the potential incompatibility of weight loss by any means with health. Available data suggest that long-term weight loss is most consistently achieved by adherence to a fat-restricted diet abundant in grains, vegetables, and fruit, along with regular physical activity, a lifestyle notably conducive to the promotion of overall health. Fad diets, potential harms of which are well characterized, should be presumed "guilty" of incompatibility with human health until or unless proved otherwise; the burden of proof should reside with proponents. In the interim, the clinical and public health communities should work to empower individuals with knowledge needed to reconcile weight control with health promotion; support policies that mitigate obesogenic environmental conditions; and offer unified resistance to the contagion of dietary propaganda.