Bariatric surgery leads to significant long-term weight loss, particularly Roux-en-Y gastric bypass (RYGB). The mechanisms underlying weight loss have not been fully uncovered. The aim of this review is to explore the changes in food preferences, as a novel mechanism contributing to weight loss, and also focus on the underlying processes modulating eating behaviour after bariatric surgery. Patients after gastric bypass are less hungry and prefer healthier food options. They develop an increased acuity to sweet taste, which is perceived as more intense. The appeal of sweet fatty food decreases, with functional MRI studies showing a corresponding reduction in activation of the brain reward centres to high-energy food cues. Patients experiencing post-ingestive symptoms with sweet and fatty food develop conditioned aversive behaviours towards the triggers. Gut hormones are elevated in RYGB and have the potential to influence the taste system and food hedonics. Current evidence supports a beneficial switch in food preferences after RYGB. Changes within the sensory and reward domain of taste and the development of post-ingestive symptoms appear to be implicated. Gut hormones may be the mediators of these alterations and therefore exploiting this property might prove beneficial for designing future obesity treatment.