Weight Loss Surgery Linked to Reduced Bone Density, Strength in Severe Obesity

Although mountains of data have been published illustrating the cardiometabolic benefits of undergoing weight loss surgery for those with overweight or obesity, new research suggests these patients could be placing themselves at increased risk of fracture later in life.

Using biomechanical computed tomography (CT) data from more than 50 patients in a prospective, nonrandomized trial, investigators determined patients who underwent sleeve gastrectomy experienced a statistically significant reduction in cortical, average, and trabecular volumetric bone mineral density (BMD) compared to those who did not undergo sleeve gastrectomy.¹

“Weight loss surgery is very effective in treating obesity and obesity-associated comorbidities in adolescents and young adults with obesity; however, it can cause loss of bone density and strength. We hope that our study raises awareness of the importance of bone health after weight loss surgery, so physicians can make sure that children eat a healthy diet with enough calcium and vitamin D and engage in weight-bearing activity to build up muscle mass, which is good for bones,” said study investigator Miriam A. Bredella, MD, MBA, a professor of radiology at Harvard Medical School and vice chair of the Department of Radiology at Massachusetts General Hospital.²

Citing a lack of previous research on the subject, the current study was led by Bredella and colleagues with the intent of exploring the effect of sleeve gastrectomy on bone strength of the lumbar spine in adolescents and young adults with severe obesity. For inclusion, participants needed to be 13-25 years of age, and have a moderate-to-severe obesity in adults and BMI equal to or greater than 120% of the 95th percentile for age and sex in adolescents.¹

To be considered for sleeve gastrectomy, patients were required to meet additional inclusion criteria, such as planning to undergo bariatric surgery, having a BMI of at least 35 kg/m2 and at least 1 obesity-related comorbidity, or have a BMI equal to or greater than 40 kg/m2. Patients were excluded from consideration if they were pregnant, had a history of medical disorders or use of medications known to affect bone metabolism, a history of smoking more than 10 cigarettes per day, and body weight greater than 200 kg.¹

Conducted at an academic medical center, patients underwent evaluations at baseline and 12 months. Investigators pointed out those in the control arm, which was the nonsurgical group, received counseling regarding diet and exercise during the study. Per study protocol, all participants underwent single-slice MRIs of the abdomen at the level of L4 and the mid-thigh for composition assessments at baseline and 12 months. Investigators noted plans to use regression analyses to estimate the effect of body composition on bone parameters and multivariable analyses to control for baseline and 12-month changes in BMI.¹

Overall, 98 subjects were screened for participation. Of these, 87 were enrolled and underwent a baseline visit. From this cohort, investigators assigned 39 patients to sleeve gastrectomy and 48 were managed non-surgically. Of the 87 patients enrolled, 72 completed the 12-month visit, including 32 from the sleeve gastrectomy group and 40 from the nonsurgical group.¹

Upon analysis, results indicated those in the sleeve gastrectomy group lost a mean of 34.3 (SD, 13.6) kg at 12 months after surgery. In contrast, weight remained unchanged in the control arm (P <.001). Further analysis suggested there were significant reductions in abdominal adipose tissue and thigh muscle area in the sleeve gastrectomy group compared with controls (P < .001). Additionally, bone strength, bending stiffness, and mean and trabecular volumetric BMD decreased in the sleeve gastrectomy group compared with controls during the study (P < .001).¹

In analyses adjusted for change in BMI, results suggested the 12-month reduction in cortical BMD was significant among the sleeve gastrectomy group compared with controls (P=.02). Investigators also highlighted reductions in strength and trabecular BMD observed in the study were associated with reductions in BMI, visceral adipose tissue, and muscle (P ≤ .03).¹

“Our study showed that sleeve gastrectomy in adolescents and young adults decreases bone strength and BMD of the lumbar spine 12 months after surgery compared with nonsurgical controls,” wrote investigators.¹

References:

1. Huber FA, Singhal V, Tuli S, et al. Biomechanical CT to Assess Bone After Sleeve Gastrectomy in Adolescents With Obesity: A Prospective Longitudinal Study [published online ahead of print, 2023 Apr 19]. J Bone Miner Res. 2023;10.1002/jbmr.4784. doi:10.1002/jbmr.4784
2. Does weight loss surgery harm adolescents' bones? EurekAlert! https://www.eurekalert.org/news-releases/986205. Published April 19, 2023. Accessed April 21, 2023.