Bariatric surgery impacts bone marrow fat and bone mass

Researchers from the University of California, San Francisco, CA, have reported that bariatric surgery can result in increases in bone marrow fat and are associated with a greater decline in bone density. The findings suggest that blood sugar metabolism and weight loss may influence marrow fat, which in turn may affect bone health.

In their study, ‘Bone Marrow Fat Changes After Gastric Bypass Surgery Are Associated With Loss of Bone Mass’, published in the Journal of Bone and Mineral Research (the official journal of the American Society for Bone and Mineral Research), the investigators sought to examine the longitudinal effects of weight loss and improved glucose homeostasis on marrow fat and assess the relationship between marrow fat and bone mineral density (BMD) changes. They hypothesised that after roux-en-y gastric bypass (RYGB) surgery, marrow fat changes are associated with BMD loss.

The study enrolled 30 obese women, stratified by diabetes status. Before and six months after RYGB, they measured the patients’ BMD by dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) and vertebral marrow fat content by magnetic resonance spectroscopy.

At baseline, those patients with higher marrow fat had lower BMD, postoperatively total body fat declined dramatically in all participants. Interestingly, the effects of RYGB on marrow fat differed by diabetes status (p=0.03): non-diabetic women showed no significant mean change in marrow fat (+1.8%, 95% confidence interval [CI] –1.8% to +5.4%, p=0.29), although those who lost more total body fat were more likely to have marrow fat increases (r=–0.70, p 0.01).

In contrast, diabetic women demonstrated a mean marrow fat change of –6.5% (95% CI –13.1% to 0%, p=0.05). Overall, those with greater improvements in haemoglobin A1c had decreases in marrow fat (r=0.50, p=0.01). Increases in IGF-1, a potential mediator of the marrow fat-bone relationship, were associated with marrow fat declines (r=–0.40, p=0.05). Spinal volumetric BMD decreased by 6.4% ± 5.9% (p < 0.01) and femoral neck areal BMD decreased by 4.3% ± 4.1% (p < 0.01).

Marrow fat and BMD changes were negatively associated, such that those with marrow fat increases had more BMD loss at both spine (r=–0.58, p< 0.01) and femoral neck (r=–0.49, p=0.01), independent of age and menopause.

The researchers concluded that their findings suggest glucose metabolism and weight loss may influence marrow fat behaviour, and marrow fat may be a determinant of bone metabolism.

"This longitudinal study adds evidence that marrow fat is a unique fat depot that may influence bone,” said Dr Tiffany Kim, lead author of the study. “Ultimately, better understanding of bone marrow fat could lead to strategies targeted to the prevention and treatment of osteoporosis, skeletal complications of bariatric surgery, and diabetic bone fragility.”