The treatment of obesity demands a negative energy balance, which obviously necessitates reducing the quantity of food intake. Yet the optimal diet composition quality for weight loss is far from known. The major controversy seems to be between choosing low-fat or low-carbohydrate diets, with additional debates on the importance of the glycemic index and the amounts of dairy products and calcium. It is evident from many large, randomized trials that the "best diet" that can suit everyone has yet to be identified. The different options for low-calorie diets should be prescribed on an individual basis, in order to best fit each patient's personal preferences. All hypocaloric regimens are suitable, as long as they work, for any given subject. The problem, of course, is long-term maintenance and adherence to an altered lifestyle.