GDF15 and obesity due to melanocortin 4 receptor deficiency: To further understand the role of GDF15 in the pathophysiology of obesity-related human diseases and to clarify whether GDF15 levels are associated with MASLD, we investigated circulating total and H-specific GDF15 levels in humans with obesity or MASLD at baseline as well as their changes during a mixed-meal test (MMT) or an oral glucose tolerance test (OGTT), respectively.