The Association of Lean Mass and Fat Mass With Peak Bone Mass in Young Premenopausal Women

Total body mass is a major determinant of bone mass, but studies of the relative contributions of lean mass (LM) and fat mass (FM) to bone mass have yielded conflicting results. This is likely because of the use of bone measures that are not adequately adjusted for body size and, therefore, not appropriate for analyses related to body composition, which is also correlated with body size. We examined the relationship between body composition and peak bone mass in premenopausal women aged 18–30 yr using both size-dependent and size-adjusted measures of bone density and body composition, as well as statistical models adjusted for size-related factors. We measured total bone mass and areal bone density using dual-energy X-ray absorptiometry, and used established formulas to calculate estimates of volumetric (size-adjusted) bone density. LM tended to be positively associated with bone both before and after adjustment for size-related factors. FM and body fat percentage, however, were positively associated with size-dependent bone measures, but adjusting for size removed or reversed this association. These findings suggest that the association between bone mass and body composition, especially FM, is dependent on the bone measures analyzed, and that determining the most appropriate size-adjustment techniques is critical for understanding this relationship.     

A 5‐Year Cohort Study of the Effects of High Protein Intake on Lean Mass and BMC in Elderly Postmenopausal Women

Long‐term effects of high dietary protein intake on muscle and bone structure in the elderly are not clear. The aim of this study was to investigate the relationship between baseline protein intake and lean mass and BMC 5 yr later in a cohort of elderly postmenopausal women. A total of 862 community‐dwelling women 75 ± 3 yr of age provided baseline data including nutrient intake assessed by a food frequency questionnaire. At 5 yr, upper arm muscle area (UAMA) and body composition using DXA were measured. Baseline protein intake was 81 ± 28 g/d (1.2 ± 0.4 g/kg/d), contributing 19 ± 3% of total energy intake. There were positive correlations between baseline protein intake and whole body and appendicular bone‐free lean mass and BMC (r = 0.14–0.18, p < 0.001) and UAMA (r = 0.08, p < 0.05). Compared with those in the lowest tertile of protein intake (<66 g/d), women in the top tertile (>87 g/d) had 5.4–6.0% higher whole body and appendicular lean mass and UAMA and 5.3–6.0% higher whole body and appendicular BMC. These effects remained after adjusting for potential confounders. However, the effect on BMC disappeared after further adjustment for lean mass. This study shows that high protein intake is associated with long‐term beneficial effects on muscle mass and size and bone mass in elderly women. The protein effect on bone may be partly mediated by its effects on muscle.