Obesity is a major risk factor of preventable deaths worldwide, with increasing rates being observed in adults and children. To understand the mechanisms of obesity development, genetically lean (Duroc strain) and obese (Rongchang strain) pigs were used to identify potential differences in muscle and adipose development patterns following consumption of an identical diet for 180 days. Lean pigs had a significantly higher lean percentage (67.79% versus 44.71%) and lower obesity index (0.68 versus 0.84) than obese pigs. They also exhibited significantly lower adipocyte volumes and higher myofibre cross-sectional areas. Quantitative polymerase chain reaction showed that lean pigs had a significantly higher expression of muscle growth-related genes and lower expression of lipogenesis-related genes. By contrast, obese pigs had higher expression of a myostatin-related gene and lower expression of lipolysis-related genes. Additionally, the mitochondrial DNA copy number was higher in the muscle and lower in adipose tissue in lean compared with obese pigs. These results indicate that lean pigs have a distinct development pattern from obese pigs, involving lipogenesis, muscle growth, and energy metabolism. This study provides a basis for exploring the mechanisms of adipose deposition and muscle growth in obesity.