Purpose of review: Low-carbohydrate diets are currently very popular with the dieting public, with many new low-carbohydrate products available on the market and in restaurants. The goal of this review is to evaluate the trend toward low-carbohydrate dieting, highlighting the important issues of safety, short-term efficacy, and long-term sustainability. Recent findings: People definitely lose weight on low-carbohydrate diets. However, there is no evidence that the weight loss can be sustained over time. In addition, there are concerns about the long-term nutritional quality and safety of the low-carbohydrate diet, especially in regards to its effects on cardiovascular health. Finally, it is clear that people successful at weight maintenance do so through changes in eating and physical activity that can be maintained for life. It is not clear whether many people can maintain a low-carbohydrate diet permanently. Summary: Weight loss occurs with low-carbohydrate diets because people restrict caloric intake on these diets, producing a short-term negative energy balance. It is less clear whether they can stay with these diets in the long term and maintain their weight loss. It is also not clear whether the diets are safe to use for years at a time. The limited data available suggest that low-carbohydrate diets may not be any better than other popular diets in helping people keep weight off permanently. A shift in our focus may be required to assist in the real challenge: keeping the weight off, not just a continuing cycle of popular diet after popular diet. © 2004 Lippincott Williams & Wilkins.