Changes in Bone Strength and Density After Roux-en-Y Gastric Bypass

In patients who underwent Roux-en-Y gastric bypass (RYGB), bone material strength index was improved 1 year after surgery despite an increase in bone turnover and lower overall areal bone mineral density (aBMD), according to study results published in Bone. These results were similar in patients with and without type 2 diabetes (T2D) before surgery.

Several previous studies have reported that RYGB, one of the most common bariatric surgical procedures, is associated with a reduction in aBMD and an increase in bone turnover and fracture risk. The goal of the current study was to explore changes in factors that can influence bone quality, bone material strength, aBMD, and bone turnover markers after RYGB, as well as to assess these changes according to T2D status.

The study enrolled 44 patients aged 18 to 65 years who were referred for RYGB at the department of morbid obesity and bariatric surgery at Oslo University Hospital in Norway. All patients had a body mass index (BMI) ≥40 kg/m² or BMI ≥35 kg/m² with obesity-related comorbidity before undergoing laparoscopic RYGB with a gastric pouch of approximately 25 mL, 150-cm antecolic alimentary limb, and 50-cm biliopancreatic limb.

After exclusion of patients not fulfilling the study criteria, the study population consisted of 34 participants, including 13 with and 21 without T2D. Estimation of bone material strength index was not possible before or after surgery in 4 patients. Levels of bone turnover markers and calciotropic hormones were estimated from fasting serum samples.

There was no correlation between bone material strength index before surgery or 1 year after RYGB with aBMD or tissue fat of the lower limb. There was an inverse association between bone material strength index before surgery and BMI (P =.010), which remained significant after adjustment for age and sex (P =.001).

Weight loss was documented in all patients 1 year after RYGB (mean, 33.9±10.9 kg; 28.3%±8.9% of total weight); BMI decreased by 11.6±4.3 points, fat mass decreased by 27.4±9.5 kg (48.8%±14.2%), and lean mass decreased by 6.3±2.5 kg (10.5%±4.1%; all P <.001). There was also improvement in exercise: the percentage of patients reporting 1 to 2 hours of physical activity a week increased from 17.6% preoperatively to 32.4% a year after surgery, and the percentage of patients reporting ≥3 hours of physical activity a week increased from 26.5% to 38.2%.

Of 13 patients with T2D before the surgery, 12 were in remission at 1 year after RYGB. Bone material strength index increased from 78.1±8.4 preoperatively to 82.0±6.4 after RYGB (mean difference, 6.3%±14.0%; P =.037). The change was not statistically different in patients with and without T2D.

In patients with T2D, a larger decrease in hemoglobin A1c was associated with a larger increase in bone material strength index (unadjusted β, -9.2; 95% CI, -16.5 to -1.9; P =.019), which remained significant after adjustment for change in BMI and age (β, -7.8; 95% CI, -15.2 to -0.38; P =.042).

There was an increase in bone turnover markers, with levels of C-terminal telopeptide of type 1 collagen (CTX) increased by 195.1%±133.6%, procollagen type 1 N-terminal propeptide (P1NP) by 109.5%±70.6%, and osteocalcin by 52.2%±28.0%. The increase in these markers did not differ significantly based on diabetes status.

The researchers reported that a year after RYGB there was a decrease in aBMD t-score at all evaluated skeletal sites; aBMD decreased by 3.9%±5.5% at the lumbar spine, 8.2%±4.6% at the femoral neck, 11.6%±4.9% at total hip, and 9.4%±3.8% in total body.

The researchers noted several study limitations, including restricted duration of follow-up, small sample size, lack of a control group, and changes in the machine used to assess BMD during the study.

“Our findings support the hypothesis that higher BMI is associated with decreased bone material strength, and implicate that surgically induced weight loss has a positive effect on bone quality,” concluded the researchers, adding that the “preservation of lean mass, maintenance of calcium, vitamin D homeostasis, and the increased physical activity noted in our population might contribute to the observed improvement in bone material strength.”

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Reference

Blom-Høgestøl IK, Mala T, Kristinsson JA, Brunborg C, Gulseth HL, Eriksen EF. Changes in bone quality after Roux-en-Y gastric bypass: a prospective cohort study in subjects with and without type 2 diabetes [published online September 12, 2019]. Bone. doi:10.1016/j.bone.2019.115069