Young Bones Weaker After Popular Weight-Loss Procedure

Adolescents and young adults with obesity who underwent sleeve gastrectomy experienced bone loss in the following years, researchers reported.

While no change was observed among those on diet and exercise alone, young people (mean age 18 years) who underwent sleeve gastrectomy had significant drops in average lumbar spine bone strength on quantitative CT scans 2 years after surgery (mean decrease -7.24 vs -728 N, P<0.001), found Miriam Bredella, MD, MBA, of Massachusetts General Hospital in Boston, and colleagues.

Surgery patients also had a significant decline in trabecular bone mineral density while virtually no change was observed in control patients (mean decrease -18.2 vs -0.02 mg/cm³), they wrote in Radiology.

According to proton MR spectroscopy, there was also a significant increase of bone marrow adipose tissue (BMAT) of the lumbar spine after sleeve gastrectomy (mean lipid-to-water ratio increase 0.10 ± 0.13, P=0.001).

“Increasingly used as an imaging biomarker, BMAT measured using MR spectroscopy can better characterize bone metabolism; studies have shown its association with increased fracture risk and reduced bone strength,” pointed out Thomas Link, MD, PhD, and Anne Schafer, MD, both of the University of California San Francisco, in an accompanying editorial.

This was a particular strength of the study, as “this is one of a few studies using an array of advanced quantitative imaging techniques to characterize bone quality and mass in the growing skeleton of adolescents after bariatric surgery,” they stated.

Sleeve gastrectomy led to weight loss: Patients who opted for surgery achieved a mean body mass index (BMI) drop of 11.9, while those who adhered to diet and exercise alone showed a 1.49-mean increase over the 2-year follow-up.

Sleeve gastrectomy patients had a 57.83 cm² average drop in abdominal visceral adipose tissue, while the control group had a significant increase of 9.07 cm². A similar pattern was seen with subcutaneous adipose tissue (-278.17 vs 46.59 cm², respectively).

Surgery patients experienced a significant drop in thigh muscle (-24.6 cm²), but controls did not.

Overall, these changes in vertebral density and strength were positively correlated with changes in BMI, but were inversely correlated with vertebral BMAT. This meant that those who lost the most weight after surgery also had the biggest bone changes.

These findings didn’t come as much of a surprise given similar data in adults, Bredella told MedPage Today.

“What was interesting is that weight-loss surgery caused an increase in fat within bones, so-called bone marrow adipose tissue, despite a significant loss of body fat,” she said. “We were also surprised that the control group, the groups of adolescents with obesity that did not undergo weight-loss surgery, did not build up bone as much as it would be expected during adolescence, implying that obesity itself has negative effects on bone health.”

“We hope that doctors and patients will be aware of the importance of bone health after weight-loss surgery,” Bredella added. “As bone loss — and osteoporosis — is painless and does not cause symptoms before one breaks a bone, it is often overlooked.”

The editorialists agreed, calling these “clinically highly important findings,” noting how adolescence and young adulthood are key times for acquiring peak bone mass necessary for later in life.

“This has potential implications for future risk of osteoporosis and fragility fractures,” Link and Schafer wrote. “While bariatric surgery is a beneficial intervention for adolescents with obesity that improves quality of life, reduces comorbidities, and increases life expectancy, rigorous attention to bone health is crucial.”

The prospective, longitudinal study followed 25 individuals who underwent sleeve gastrectomy, the most popular form of bariatric surgery. As is typical with a bariatric surgery cohort, the vast majority were female (80%). These individuals were compared with 29 individuals who adhered to diet and exercise counseling without surgery.

At baseline, BMI was 46.9 and 43 in the surgery and controls groups, respectively.

In the 2 years after surgery, patients had a significant increase in phosphorus levels, with no changes in calcium, vitamin D, or parathyroid hormone.

Study limitations included the lack of randomization and the short follow-up period.