Losing weight before undergoing Roux-en-Y gastric bypass (RYGB) surgery may reduce liver fat content and size thereby improving surgical outcomes. This study aims to investigate whether a 2-week or 6-week pre-operative liquid formula low-calorie diet (LCD) reduces liver fat further than a conventional food diet prior to RYGB using magnetic resonance imaging (MRI). The hypothesis is that the 2-week and 6-week liquid formula LCD will reduce liver fat further than the conventional food pre-operative diet.