Does being overweight affect your bone density?

Being overweight generally increases the load on the skeleton, which can slightly raise bone density. Most observational studies do indeed show higher bone density values in people with obesity compared with people of a healthy weight. Yet this protective effect is far more limited than long believed, because it says nothing about the quality of bone at the microscopic level or about actual fracture risk.

Where the fat is located makes a big difference. A lot of abdominal fat (so-called visceral fat deep in the abdominal cavity) is beneficial up to a point, but at higher amounts the bone density of the femur actually decreases and the risk of osteoporosis rises in older people. People who have a relatively high amount of fat in relation to their body weight have lower bone density at multiple sites. In the group with the highest fat-to-weight ratio, lumbar bone density was on average 0.08 g/cm2 lower than in the group with the lowest ratio. That difference is clinically relevant.

Chronic low-grade inflammation, which is more common in obesity, also likely damages bone directly. Fat cells that develop in the bone marrow displace bone cells, which can lead to loss of bone mass. This has so far been demonstrated mainly at the biological level, but the mechanism is biologically plausible.

Losing weight is good for overall health, but it has a downside for the skeleton: rapid and substantial weight loss often goes hand in hand with loss of bone density. Bariatric surgery (gastric reduction) measurably lowers femoral neck bone density on average, even years after the procedure. Weight-loss medications such as semaglutide appear to be neutral for bone so far, although weight loss also causes some loss of muscle mass, which can have an indirect effect. Moderate and gradual weight loss, combined with strength training and adequate calcium and vitamin D, keeps bone density much better preserved.

In obese older women, resistance training did not increase bone density, but the group that did nothing lost measurable bone over 24 weeks. Exercise therefore protects, even when it does not actively increase bone density.