Background:  Obese individuals often present comorbidities while they appear protected against the development of osteoporosis. However, few and contradictory data are now available on skeletal modifications in obese patients. The aim of this study was to characterise bone mineral density (BMD) in overweight (BMI > 25 < 29.9) and obese (BMI > 30) patients.

Methods:  We selected 398 patients (291 women, 107 men, age 44.1 + 14.2 years, BMI 35.8 + 5.9 kg/m2) who underwent clinical examination, blood tests and examination of body composition. Subjects with chronic conditions or taking medications interfering with bone metabolism, hormonal and nutritional status and recent weight loss were excluded.

Results:  Interestingly, 37% (= 146) of this population showed a significantly lower than expected lumbar BMD: 33% (= 98) of women showed a T-score −1.84 ± 0.71, and 45% (= 48) of men showed a T-score −1.88 ± 0.64. When the population was divided into subgroups based on different BMI, it was noted that overweight (BMI > 25 < 29.9) was neutral or protective for BMD, whereas obesity (BMI > 30) was associated with a low bone mass, compatible with a diagnosis of osteoporosis. No differences were observed in hormones and lipid profiles among subgroups.

Conclusions:  Our results indicate that a subpopulation of obese patients has a significant low lumbar BMD than expected for age. Thus, a careful characterisation of skeletal metabolism might be useful in all obese individuals to avoid fragility fractures later in life.