Dietetic intervention has the following aims: to achieve a negative energy balance, obtain a healthy weight in the obese person and achieve the installation of healthy eating habits in order to maintain weight loss in the long term. Considering dietetic treatment of obesity as a process that is maintained for long periods of time, dietetic intervention should be carried out depending on the physio-pathological and psycho-social characteristics of the obese person. Besides, dietetic therapy should be balanced, healthy and adapted to the eating preferences of the patient. Over the years, due to need and the quest for rapid weight loss, magic diets have been occasioned, created and invented that have become popular and that lack proven efficacy and scientific rigour. This paper makes reference to a balanced hypocaloric diet and reviews the slimming diets that are best known and most used by the obese and/or overweight population.