The main aim of obesity surgery is to change the dietary habits of morbidly obese patients. These are patients whose dietary habits nutritionists and psychologists have not been able to change during previous decades. The history of this surgery can teach us many important lessons. For example, procedures that have focused on effecting a malabsorptive state, but without addressing any behavioural mechanism for weight control, such as jejunoileal bypass, have failed. On the other hand, those that have centered on only addressing behavioural issues, the purely restrictive, are also difficult for patients to comply with and also have a high failure rate. To facilitate a change in the nutritional behaviour of morbidly obese patients which can lead to the loss of an adequate amount of weight, and which could be maintained in the long term is difficult. We need to stimulate changes that can be easily followed by the patient, and at the same time, provoke minimal medium and long term alterations in their nutritional state. To achieve and maintain this aim efficiently, it is necessary that the patients have confidence in and respect the physician, so that they can follow strictly their medical advice.