Obesity and bone health: reconciling the density-fragility paradox.

The relationship between obesity and bone health is increasingly recognized as complex and paradoxical. Despite higher bone mineral density (BMD) in individuals with obesity, fracture risk is not uniformly reduced. Instead, fractures tend to occur more frequently at peripheral sites such as the ankle, humerus, and tibia, indicating a mismatch between BMD and true bone strength. In the early stages of weight gain, mechanical loading and adipose-derived hormonal factors may promote bone formation. However, these effects are progressively counterbalanced by chronic inflammation, oxidative stress, and marrow adiposity, which impair bone quality and compromise microarchitecture. Conventional dual-energy X-ray absorptiometry (DXA), while central to clinical assessment, cannot capture these changes and may overestimate skeletal strength in the presence of excess soft tissue. Emerging tools such as trabecular bone score and high-resolution peripheral quantitative computed tomography provide additional insights into bone quality, including microarchitecture and cortical porosity, particularly in individuals with type 2 diabetes. Obesity is also associated with vitamin D deficiency, impaired muscle function, and sarcopenic phenotypes, further increasing fracture risk. Bariatric surgery introduces additional challenges by accelerating bone turnover and loss. This review highlights the need to move beyond BMD alone and adopt comprehensive, individualized approaches to fracture risk assessment and management in obesity.