 Rodents with mutations in the leptin gene have been widely studied to understand the mechanisms behind obesity. These rodents are known to have reduced energy expenditure which was previously thought to be caused by increased metabolic efficiency. However, recent research suggests that reduced energy expenditure is also an important factor in the development of obesity in these rodents. Studies show that mice have similar milk intake to normal mice, despite consuming more calories overall. Additionally, above mice require less food to maintain their weight compared to normal mice, suggesting that they have a low arresting metabolism. Finally, above mice have been found to have a low arresting metabolic rate per unit body weight, indicating that they burn fewer calories for each pound of body mass. Taken together, these findings suggest that reduced energy expenditure plays a role in the development of obesity in leptin pathway mutants. This article was authored by Paul Trehearn and Jonathan R. S. Arch.