"Success" in dieting interventions has traditionally been defined as weight loss. It is implicit in this definition that losing weight will lead to improved health, and yet, health outcomes are not routinely included in studies of diets. In this article, we evaluate whether weight loss improves health by reviewing health outcomes of long-term randomized controlled diet studies. We examine whether weight-loss diets lead to improved cholesterol, triglycerides, systolic and diastolic blood pressure, and fasting blood glucose and test whether the amount of weight lost is predictive of these health outcomes. Across all studies, there were minimal improvements in these health outcomes, and none of these correlated with weight change. A few positive effects emerged, however, for hypertension and diabetes medication use and diabetes and stroke incidence. We conclude by discussing factors that potentially confound the relationship between weight loss and health outcomes, such as increased exercise, healthier eating, and engagement with the health care system, and we provide suggestions for future research.