Fat-free mass or lean tissue mass includes nonskeletal muscle components such as the fat-free component of adipose tissue fat cells. This fat-free component of adipose tissue may need to be taken into consideration when large changes in body fat occur following a weight loss intervention. It is not uncommon to see a loss of lean mass with interventions designed to promote the loss of large amounts of fat mass. However, after eliminating the influence of the fat-free component of adipose tissue on dual-energy x-ray absorptiometry (DXA)-derived lean mass, the original loss of lean mass is no longer observed or is markedly reduced. This suggests that the majority of the lean mass lost with dieting may be the fat-free component of adipose tissue. To accurately estimate the change in lean tissue, eliminating the fat-free adipose tissue from DXA-derived lean mass is needed when large changes in body fat occur following an intervention.