The Adibox Study: Adiposity and Bone Metabolism: Effects of Exercise-induced Weight Loss in Adolescents with Obesity

Introduction: This program of research targeted the impact of an 8-month weight loss intervention induced by physical activity and nutrition on bone health in adolescents with obesity. The overall aim of this thesis was to examine the impact of a lifestyle weight loss intervention on the bone parameters in adolescents with obesity.

Method: Sixty-five adolescents were recruited: 31 (6 males) adolescents with obesity in the weight loss intervention (age: 13.61 (1.27)), 23 normal weight (NW) adolescents (age: 15.90 (0.43)) and 11 (4 males) adolescents with obesity in another control group (14.02 (1.39)). Primary outcomes targeted bone densitometry (whole body, spine, hip DXA). Secondary outcomes included body composition, bone geometry and strength (hip structural analysis) and bone biomarkers (procollagen type 1 N-terminal propeptide (P1NP), C telopeptide (CTx) estradiol, leptin). Data were collected at baseline, 4 months and 8 months. Data were adjusted for body weight, fat mass and lean mass changes.

Results: Compared with the NW controls, adolescents with obesity displayed lower unadjusted and adjusted bone density. Following successful weight loss (~ -11%) adolescents with obesity increased whole body (%Ob Δ 3.22 (3.58) pp<0.001) and lumbar spine (%Ob Δ 6.27 (12.45) p=0.014) BMD. However, values remain lower than their NW peers after adjustment to body weight changes. After the weight loss intervention, compromised estimates of fracture risk remained especially at the narrow neck (buckling ratio (BR) 8.25 (2.00) p=0.005), despite positive adaptations of some geometric properties (i.e. NN CSA, NN Z). Also, bone accretion changes in adolescents with obesity followed an androgen-like adaptation demonstrated by periosteal expansion (% NW Δ 0.69 (3.71); Ob Δ 1.67 (9.11)) and endocortical resorption (% NW Δ -2.11 (11.79); Ob Δ 4.42 (10.56)). Among the intervention group, differences in bone markers favoured formation during the first 4 months and favoured resorption in the remaining months.

Conclusion: Bone fragility in adolescents with obesity was demonstrated by (1) baseline and post intervention lower whole body and regional BMD than NW controls, (2) post-intervention higher fracture risk index at the narrow neck, (3) bone biomarkers showing reduced z-scores, uncoupling indices and qualitative representations of the distribution of bone remodeling. Future investigations of links between bone and obesity during adolescence can be well informed by the results of this thesis.