The health benefits of metabolic/bariatric surgery (MBS) are associated not only with the improvement in comorbidities but also with the reduction in mortality. These remarkable health outcomes contributed to the increase in the use of MBS as a therapeutic approach for severe and complex obesity. MBS is also indicated in metabolically challenged patients. In this chapter, we summarize the main insights on the medical nutritional therapy and management of MBS in patients suffering from chronic liver and kidney disease, pregnancy, and vegetarians. We will provide insights into certain practical aspects that underscore the importance of establishing a therapeutic alliance and promoting long-term patient commitment. The development of a patient-centred programme will help prevent, identify, and manage the risk of nutritional complications and optimize outcomes.