The greatest change that occurs after any bariatric operation is to the patient’s diet and the role of a dietician both before and after surgery cannot be understated. Important guidance is essential for patients transitioning from a usually unhealthy and excessive diet to one that is replete with components essential to a healthy lifestyle yet possible within the restrictions imposed by surgery. Preoperatively, patients require a 2-3 week period of a Very Low Energy Diet (VLED) most importantly to decrease the size and turgidity of the liver thus facilitating safe surgery. Following the operation, given patients’ intake is restricted, the choice of food type is very important to ensure adequate nutrients, fluid and protein intake so healing can occur without difficulty. Patients take time to learn which foods are easier to consume during the early post-operative phase and careful guidance from their dietician ensures they remain on track. Additional supplements may be needed such as protein, Vitamin B12, Folate, Iron, Calcium, Copper, Zinc and fat-soluble vitamins (ADEK). Regular blood tests are essential. A daily multivitamin is also recommended lifelong.