Literature review on the use of small rodents as animal models to study obesity induced by fat‐rich diets, with a focus on their similarities and differences to human obesity. The review examines physiological, hormonal, and behavioral mechanisms involved in fat‐induced obesity, including nutrient utilization efficiency, hormonal roles (leptin, ghrelin, insulin), and eating behaviors. The chapter also discusses the potential for reversing obesity and provides recommendations for future research and study design in animal models of obesity. The gene discussed is LEP; the disease is obesity due to melanocortin 4 receptor deficiency.