About 70% of obese people have metabolic dysfunction-associated steatotic liver disease (MASLD), also found in lean individuals. Effective treatments for MASLD may not change body weight or even cause weight gain. A review in 'The Lancet Diabetes & Endocrinology' discusses MASLD heterogeneity, its pathogenesis, outcomes, and metabolism-based treatment responses, emphasizing precision medicine for risk prediction, prevention, and treatment. MASLD is a global epidemic, linked to cirrhosis, hepatocellular carcinoma, type 2 diabetes, cardiovascular disease, chronic kidney disease, and extrahepatic cancers. Researchers identify three major pathomechanisms: genetic, metabolic (hepatic de novo lipogenesis), and metabolic (adipose tissue dysfunction). Future personalized treatments and lifestyle modification programs could target these subtypes.