Bone metabolism increased after gastric bypass

Last Updated: 2016-11-22

By Marilynn Larkin

NEW YORK (Reuters Health) - Bone remodeling activation is significantly higher after Roux-en-Y gastric bypass surgery compared with surgical sleeve gastrectomy, researchers in Finland report.

"Bariatric surgery results in rapid weight loss and beneficial metabolic effects, but may have negative effects on the skeleton," Dr. Kaisa Ivaska of the University of Turku and colleagues write in Bone, online November 2.

To investigate, the team enrolled 46 morbidly obese patients (average age, 45; average BMI, 42.1). At baseline, 19 had type 2 diabetes and 27 did not. A total of 21 underwent Roux-en-Y gastric bypass (RYGB) and 25 had sleeve gastrectomy (SG).

Bone turnover markers, including CTX, PINP, TRAcP5b, totalOC and ucOC were measured before and six months after surgery. Seven RYGB and 14 SG patients also had volumetric bone mineral density (vBMD) at the lumbar spine measured, as well as vertebral bone marrow (VBM) fat.

The team also recruited 25 non-obese individuals (average age, 46; average BMI, 23.0) as controls, whose bone turnover markers were assessed at a single visit.

All obese participants had significantly lower bone turnover at baseline compared with controls. Specifically, the PINP/CTX ratio was elevated and the CTX/TRAcP5b ratio was decreased in obese patients at baseline, "suggesting low resorptive activity in obesity," the authors note.

After surgery-induced weight loss, both ratios reversed and became close to those of controls in all patients. The authors suggest that "bone metabolism, which is suppressed in morbid obesity, is activated after bariatric surgery, resulting in high overall post-operative bone turnover."

Bone remodeling activation was significantly higher after RYGB compared with SG, especially in those whose type 2 diabetes went into remission after weight loss.

Among the 19 (41%) of patients who had type 2 diabetes before surgery, 58% went into remission post-surgery. Bone markers increased similarly in patients without diabetes and those who went into remission postoperatively, whereas only a modest increase was seen in patients who remained diabetic.

There were no changes in vBMD or VBM fat in any patients six months post-surgery.

Dr. Ivaska and her co-author Dr. Riku Kiviranta, also at Turku, told Reuters Health, "Morbid obesity and especially type II diabetes suppress bone turnover. Bariatric surgery induces activation of bone turnover, especially in patients whose type II diabetes is in remission after surgery."

"Based on our data, the choice of surgical approach does have an impact on the post-surgery activation of bone turnover," she said by email. "Extended studies are needed to assess whether the two surgical approaches have different effects on skeletal health in the long term."

Dr. Michael Russo, a bariatric surgery specialist at MemorialCare Center for Obesity at Orange Coast Memorial Medical Center in Fountain Valley, California, told Reuters Health, "Bone turnover is significantly compromised in obesity . . . and is reflective of the suboptimal hormone-mediated metabolic state of the obese patient."

"After bariatric surgery, the body's bone turnover rate increases back to a more normal rate, which is another example of the improved metabolic state that we see in post-bariatric patients," he said by email. "This change is also the main contributor to weight loss."

Dr. Luga Podesta, director of sports medicine at St. Charles Orthopedics in Port Jefferson, New York, said the improvement in bone remodeling "means there should be less risk of potential bone injuries such as fractures after bariatric surgery."

"Patients will be able to exercise and become more physically active," Dr. Podesta told Reuters Health by email, "which in turn will be beneficial in promoting further weight loss and improving cardiovascular fitness."

SOURCE: http://bit.ly/2gg0WOY

Bone 2016.