People with type 2 diabetes have an increased risk of bone fractures, which may be partly because of altered bone marrow adipose tissue (BMAT) composition. A recent manuscript, published by Kim et al. in the latest issue of Bone Reports, went on to investigate whether the Roux-en-Y gastric bypass (RYGB) surgery, which is known to improve the glycemic status of patients, alters the unsaturated lipid composition of bone marrow, and whether these changes differ by diabetes status or by anatomic skeletal location.
Thirty obese adult women (>25 years of age) that were scheduled for an upcoming gastric bypass procedure, were recruited from two academic bariatric surgery centres in San Francisco. Enrolment was stratified by diabetes status and bone marrow adipose tissue (BMAT) was measured by magnetic resonance spectroscopy at the spine (n=30) and tibia (n=19). The total marrow fat content as well as the unsaturated lipid index were calculated. Bone mineral density, BMI, whole body fat, lean mass, visceral adipose tissue area and serum levels for haemoglobin A1c (HbA1c), 25 hydroxyvitamin D and sclerostin, were also measured at baseline and 6 months after gastric bypass.
Findings showed that although at baseline BMAT parameters were similar between those with and without diabetes, six months after RYGB surgery there was a significant interaction between diabetes status and changes in both vertebral marrow fat content (p = 0.02) and the unsaturated lipid index (p < 0.01). In diabetic patients, there was a trend towards a decline in marrow fat content (-4.3 % ± 8.2 %, p = 0.09) and a significant increase in the unsaturated lipid index (+1.1 % ± 1.5 %, p = 0.02). No significant changes in BMAT parameters were observed in women without diabetes. Furthermore, no differences were observed between women with and without diabetes at the tibial marrow fat content or composition. Finally, changes in the unsaturated lipid index were inversely correlated with haemoglobin A1c changes (r = -0.47, p = 0.02), regardless of diabetes status.
Authors concluded that gastric bypass-induced weight loss led to longitudinal changes in the vertebral but not tibial, BMAT content and composition and that these changes were different for women with versus without diabetes. They also noted that changes in the unsaturated lipid index at the spine correlated with glycemic improvements.