Gastric bypass, not banding, associated with enhanced bone turnover

Last Updated: 2015-12-09

By Will Boggs MD

NEW YORK (Reuters Health) - Patients with type 2 diabetes who underwent Roux-en-Y gastric bypass (RYGB) had increased levels of bone-remodeling markers, whereas those had laparoscopic adjustable gastric banding (LAGB) did not, according to a new study.

RYGB has been associated with declines in bone density of 5% to 10% at the hip and 3% to 6% at the spine within the first one to two years postoperatively, researchers note in The Journal of Clinical Endocrinology & Metabolism, online November 24. Less is known about bone changes after LAGB.

Dr. Elaine W. Yu from Massachusetts General Hospital, Harvard Medical School, Boston, and colleagues compared postoperative levels of type 1 cross-linked C-telopeptide (CTX), a marker of bone resorption, and serum procollagen type 1 N-terminal propeptide (P1NP), a marker of bone formation, in 11 RYGB and eight LAGB patients who participated in the SLIMM-T2D trials.

Fasting CTX levels increased by 221% one year after RYGB, but did not change significantly after LAGB. Fasting P1NP levels were also significantly higher one year after RYGB, rising by 93%, while there was an insignificant drop in the LAGB group.

Fasting levels of peptide YY (PYY), an anorexigenic hormone that may have catabolic effects on bone, were significantly higher one year after RYGB but not after LAGB.

Hemoglobin A1c improved significantly only after RYGB, and this group experienced greater weight loss by one year compared with the LAGB group.

After RYGB, postprandial CTX declined more dramatically than after LAGB, whereas postprandial PYY increased more after RYGB than after LAGB.

Changes in fasting and postprandial CTX were not significantly associated with weight loss.

"Future studies should further investigate connections between GI hormones and bone as a potential mechanism of skeletal changes after RYGB surgery," the researchers conclude. "Finally, it will be important to conduct large prospective studies to examine differential changes in bone density after bariatric surgery. These studies will provide clinically important information for physicians and patients who are weighing potential risks of these highly effective weight loss surgeries."

Dr. Christian Muschitz, head of the osteoporosis unit at St. Vincent Hospital, Medical University of Vienna in Austria, told Reuters Health by email, "Bariatric surgery causes early and sustained hormonal changes with negative influence on bone health. Patients after RYGB need a specific program after the surgery."

Dr. Muschitz and colleagues recently reported that vitamin D loading and ongoing vitamin D, calcium, and BMI-adjusted protein supplementation in combination with physical exercise decelerated the loss of bone mineral density and lean body mass after bariatric surgery. The regimen was also associated with less pronounced increases in bone turnover markers, they found.

Dr. Yu did not respond to a request for comments.

SOURCE: http://bit.ly/1m9Z5MZ

J Clin Endocrinol Metab 2015.