We report a case of post bariatric surgery by laparoscopic sleeve gastrectomy who presented with post-surgical poor oral tolerance and high anion gap metabolic ketoacidosis, who was initially misdiagnosed with diabetic ketoacidosis and treated with volume supplementation without improvement. The metabolic derangements were found to be caused by starvation ketoacidosis, which was then treated with glucose supplementation, and the anion gap quickly closed. Moreover, this patient also presented with non-pancreatitis lipase elevation. This case highlights the recognition and management of post-bariatric surgery starvation ketoacidosis; additionally, clinicians should be vigilant about the interpretation and management of elevated lipase without clinical pancreatitis.