INS and obesity due to melanocortin 4 receptor deficiency: Each method has different limitations: MCD diet-fed rats do not develop obesity (they even get weight loss) and insulin resistance; CD diet induces liver steatosis and fibrosis without significant weight change; intragastric overfeeding needs specific training and equipment; high sucrose diet may induce mild liver inflammation without significant steatohepatitis and fibrosis; high fat diet may require longer feeding period to induce fatty liver diseases.