Poor diet and physical inactivity, the two major contributors to the development of overweight and obesity, have recently been identified as the second most common actual cause of death in the United States. With the increasing awareness of the strong link between obesity and chronic disease, in particular cardiovascular disease, a myriad of diets have surfaced and many of them claim weight loss depends more on the macronutrient composition of the diet than the number of calories consumed. Long-term outcome data, particularly cardiovascular outcome data, on these diets are sparse. This article summarizes previous and recent reports of popular and aggressive diets, such as low-carbohydrate diets, low-fat diets, and very low-calorie diets, addressing their effects on weight loss and focusing on their effects on lipids and lipoproteins.