We couldn't notinclude this one last myth. "Muscle weighs more than fat" is a common line that has been heard in the fitness community over the past years. In a preview interview, NASM-certified personal trainer Gabbi Berkow, MA, CDN, told POPSUGAR that a pound of muscle weighs the same as a pound of fat (a pound is a pound). But, muscle is denser than fat, she said. "It has more water, protein, carbohydrates, and fats in it than fat does, but it takes up less space. Since density equals weight divided by volume, the same amount or weight of muscle takes up less space than fat." That's why, she explained, gaining muscle is often associated with losing inches but not necessarily losing weight on the scale.