Metabolic dysfunction-associated steatotic liver disease (MASLD) affects around 25% of the global population. It is expected to be the primary cause of end-stage liver disease and liver transplantation. Obesity is regarded as a major risk factor for MASLD. Still, there is a subset of MASLD patients who do not exhibit obesity-related traits, and this group is frequently neglected in clinical workups. It cannot be detected and treated immediately. More and more research has shown that MASLD is a multi-systemic disease that is linked not only to type-2 diabetes but also to end-stage liver disorders like cirrhosis, liver failure, hepatocellular carcinoma, cardiovascular disease, and chronic kidney disease. Furthermore, lean MASLD patients may be more likely to develop liver fibrosis and end-stage liver disease, as well as a higher risk of cardiovascular disease and mortality.