[Obesity, fat and bones: friends or foes ?].

Low fat mass is associated with an increased risk of fracture because of low bone mineral density (BMD) and altered bone micro-architecture. Conversely, overweight and obese patients also have an increased risk of fracture, particularly of the humerus and ankle, despite greater BMD. Visceral abdominal fat, which is the most metabolically active, may be associated with poorer quality of bone tissue properties, as suggested in diabetes. Other factors may contribute to higher fracture risk in overweight patients, notably higher frequency of falls and lower bioavailability of vitamin D stoked in fat. Thus, fat mass and its distribution should be taken into account beyond BMD and classical clinical risk factors in the assessment of fracture risk.