Bone metabolism after bariatric surgery

Abstract

Bariatric surgery is a popular and effective treatment for severe obesity but may have negative effects on the skeleton. This review summarizes changes in bone density and bone metabolism from animal and clinical studies of bariatric surgery, with specific attention to Roux-en-Y gastric bypass (RYGB), adjustable gastric banding (AGB), and sleeve gastrectomy (SG). Skeletal imaging artifacts from obesity and weight loss are also considered. Despite challenges in bone density imaging, the preponderance of evidence suggests that bariatric surgery procedures have negative skeletal effects that persist beyond the first year of surgery, and that these effects vary by surgical type. The long-term clinical implications and current clinical recommendations are presented. Further study is required to determine mechanisms of bone loss after bariatric surgery. Although early studies focused on calcium/vitamin D metabolism and mechanical unloading of the skeleton, it seems likely that surgically induced changes in the hormonal and metabolic profile may be responsible for the skeletal phenotypes observed after bariatric surgery.

Keywords: BARIATRIC SURGERY; BIOCHEMICAL MARKERS OF BONE TURNOVER; DXA; OBESITY.

© 2014 American Society for Bone and Mineral Research.

Figures

Figure 1. Diagram of bariatric surgery procedures and outcomes

The diagram depicts the surgical procedure for Roux-en-Y gastric bypass (RYGB), adjustable gastric band (AGB), and sleeve gastrectomy (SG) (Adapted with permission from Pories WJ, JCEM 2008, 93(11):S89–S96). Dark grey shading indicates the post-surgical gastrointestinal route for passage of food. Dotted lines represent the excised gastric fundus after SG. The table below summarizes the worldwide popularity (6), average excess weight loss, and improvements in comorbidities associated with the different procedures (1).

Figure 2. Percent change in spine bone mineral density (BMD) after bariatric surgery

Graphical summary of data from longitudinal studies of bariatric surgery, by surgery type. Unless otherwise indicated, percent change is measured by DXA at lumbar spine from preoperative baseline to postoperative time-point after RYGB, SG, or AGB. Study size (n) and study length (mo = months, yr = years) are noted. In one study, percent change as measured by quantitative computed tomography (QCT) is also reported. * statistically significant compared with baseline (within-group comparison) ^ statistically significant compared with control group (between-group comparison) a: vertebral BMD was assessed by total body DXA b: values are estimated from published figures

Figure 3. Percent change in hip bone mineral density (BMD) after bariatric surgery

Graphical summary of data from longitudinal studies of bariatric surgery, by surgery type. Unless otherwise indicated, percent change is measured by DXA at the total hip from preoperative baseline to postoperative time-point after RYGB, SG, or AGB. Study size (n) and study length (mo = months, yr = years) are noted. In selected studies, alternative imaging techniques (QCT = quantitative computed tomography) or alternative hip sites (i.e. femoral neck) are noted. * statistically significant compared with baseline (within-group comparison) ^ statistically significant compared with control group (between-group comparison) a: % change in femoral neck BMD is shown as total hip BMD results were not reported