The weight of a pound of muscle and a pound of fat is the same. However, muscle is denser than fat, meaning it takes up less volume than an equal amount of fat. This explains why someone can look slimmer without a significant drop in weight, and why 10 pounds of muscle on a person looks very different than 10 pounds of fat, even though both amounts of weight are the same. Therefore, it is important to monitor body composition, which provides information about your internal tissue makeup, rather than weight itself.