Bariatric surgery is increasingly popular but may lead to metabolic bone disease.

The objective was to determine the rate of bone loss in the 24 months after Roux-en-Y gastric bypass.

This was a prospective cohort study conducted at an academic medical center.

The participants were adults with severe obesity, including 30 adults undergoing gastric bypass and 20 nonsurgical controls.

We measured bone mineral density (BMD) at the lumbar spine and proximal femur by quantitative computed tomography (QCT) and dual-energy x-ray absorptiometry at 0, 12, and 24 months. BMD and bone microarchitecture were also assessed by high-resolution peripheral QCT, and estimated bone strength was calculated using microfinite element analysis.

Weight loss plateaued 6 months after gastric bypass but remained greater than controls at 24 months (−37 ± 3 vs −5 ± 3 kg [ mean ± SEM]; P < .001). At 24 months, BMD was 5–7% lower at the spine and 6–10% lower at the hip in subjects who underwent gastric bypass compared with nonsurgical controls, as assessed by QCT and dual-energy x-ray absorptiometry (P < .001 for all). Despite significant bone loss, average T-scores remained in the normal range 24 months after gastric bypass. Cortical and trabecular BMD and microarchitecture at the distal radius and tibia deteriorated in the gastric bypass group throughout the 24 months, such that estimated bone strength was 9% lower than controls. The decline in BMD persisted beyond the first year, with rates of bone loss exceeding controls throughout the second year at all skeletal sites. Mean serum calcium, 25(OH)-vitamin D, and PTH were maintained within the normal range in both groups.

Substantial bone loss occurs throughout the 24 months after gastric bypass despite weight stability in the second year. Although the benefits of gastric bypass surgery are well established, the potential for adverse effects on skeletal integrity remains an important concern.