**1. Introduction**

Bariatric surgery (BS) has proven to be an effective treatment for weight loss, reducing obesity associated comorbidities, improving quality of life, and reducing mortality rates [1, 2]. The increasing amount of evidence on the benefits of BS has contributed to its increased popularity over the last decade [1]. Despite the proven benefits of BS, it also carries the risk of short- and long-term complications. An important complication is the nutritional and micronutrient deficiencies. Nutritional deficiencies can present with a wide range of clinical manifestations, depending on the specific nutrients/micronutrients that are involved, the severity, and the duration of the deficiency states. Additionally, these deficiencies can worsen over time, leading to severe consequences, such as anemia (iron, folate, B12), peripheral neuropathy (folate, B6, B12, copper), Wernicke encephalopathy (B1) and metabolic bone disease (vitamin D, calcium). Therefore, lifelong screening of individuals who had undergone bariatric surgery is critical to identify these complications and treat them effectively to ensure long-term success. This chapter will provide a comprehensive review of these nutritional complications. The chapter will also furnish information about the recommended micronutrient supplementations and nutritional follow-up.
