Obesity reduces bone size and strength

It looks like contrary to popular belief, obese people are not “just big boned”  In fact, the following study shows a smaller bone size and strength for obese college age women versus those with less that 32% body fat. 

American Journal of Clinical Nutrition, Vol. 86, No. 5, 1530-1538, November 2007

Is adiposity advantageous for bone strength? A peripheral quantitative computed tomography study in late adolescent females1,2,3

Norman K Pollock, Emma M Laing, Clifton A Baile, Mark W Hamrick, Daniel B Hall and Richard D Lewis 1 From the Departments of Foods and Nutrition (NKP, EML, CAB, and RDL) and Statistics (DBH), The University of Georgia, Athens, GA, and the Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, GA (MWH)

Background: Whereas excess adiposity is presumed to be advantageous for the skeleton, studies investigating relations between bone strength and fat during youth have been equivocal.

Objectives: Relations of percentage body fat (BF) and bone strength indexes were assessed in late adolescent females, taking into consideration surrogates of muscle force [ie, muscle cross-sectional area (MCSA) and bone length]. Bone measurements in the normal- and high-fat groups were also compared.

Design: Late adolescent females (n = 115; aged 18.2 ± 0.4 y) participated in this cross-sectional study. Fat-free soft tissue mass, fat mass, and percentage BF were measured with the use of dual-energy X-ray absorptiometry. Tibial and radial peripheral quantitative computed tomography measurements were taken at the 4% (trabecular bone), 20% (cortical bone), and 66% (for measurement of MCSA) sites from the distal metaphyses.

Results: Percentage BF was inversely related to radial cortical bone area, total bone cross-sectional area (CSA), cortical bone mineral content (BMC), periosteal circumference, and strength-strain index (SSI) (20% site; all P < 0.05). After control for MCSA and limb length, negative relations remained between percentage BF and radial measurements and were also observed at the tibia (20% site). Unadjusted bone measures were not different between groups. After control for MCSA, the high- compared with the normal-fat group had lower bone measures at the 20% site (cortical bone area and cortical BMC at the tibia, total bone CSA at the radius, and SSI at both the tibia and radius; P < 0.05 for all).

Conclusion: Excess weight in the form of fat mass does not provide additional benefits, and may potentially be negative, for adolescent bone.

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