Fat mass is not beneficial to bone in adolescents and young adults.

CONTEXT Although muscle mass is beneficial to bone, studies on the effect of fat mass on bone have yielded conflicting results. OBJECTIVE The aim of this study was to assess the relations between lean and fat mass and bone structure. DESIGN This study was cross-sectional. SETTING The study was conducted in a general community. SUBJECTS Subjects included 300 healthy sexually mature adolescents and young adults (150 males and 150 females) between the ages of 13 and 21 yr. MAIN OUTCOME MEASURE We investigated the relation between dual-energy x-ray absorptiometry (DXA) measures of total body fat and lean mass and bone values obtained with DXA (legs and lumbar spine bone mineral density and bone mineral content) and computed tomography (CT) (cross-sectional and cortical bone areas of the femurs and cross-sectional area and cancellous bone density of the vertebrae). RESULTS Simple and multiple linear regression analyses showed significant positive relations between DXA lean mass and all CT and DXA measures of bone in the axial and appendicular skeletons (all P < 0.005). In contrast, whereas Pearson correlations between DXA measures of fat mass and bone parameters were generally positive, multiple regression analyses showed that fat mass, after accounting for lean mass, trunk height/leg length, had a negative, or no, correlation with CT and DXA values for bone. CONCLUSIONS Our findings provide compelling evidence that, despite increased mechanical loading and independent of lean mass, adipose tissue is not beneficial to bone structure.