Bone Response to Weight Loss Following Bariatric Surgery

Abstract

Obesity is a global health challenge that warrants effective treatments to avoid its multiple comorbidities. Bariatric surgery, a cornerstone treatment to control bodyweight excess and relieve the health-related burdens of obesity, can promote accelerated bone loss and affect skeletal strength, particularly after malabsorptive and mixed surgical procedures, and probably after restrictive surgeries. The increase in bone resorption markers occurs early and persist for up to 12 months or longer after bariatric surgery, while bone formation markers increase but to a lesser extent, suggesting a potential uncoupling process between resorption and formation. The skeletal response to bariatric surgery, as investigated by dual-energy X-ray absorptiometry (DXA), has shown significant loss in bone mineral density (BMD) at the hip with less consistent results for the lumbar spine. Supporting DXA studies, analyses by high-resolution peripheral quantitative computed tomography (HR-pQCT) showed lower cortical density and thickness, higher cortical porosity, and lower trabecular density and number for up to 5 years after bariatric surgery. These alterations translate into an increased risk of fall injury, which contributes to increase the fracture risk in patients who have been subjected to bariatric surgery procedures. As bone deterioration continues for years following bariatric surgery, the fracture risk does not seem to be dependent on acute weight loss but, rather, is a chronic condition with an increasing impact over time. Among the post-bariatric surgery mechanisms that have been claimed to act globally on bone health, there is evidence that micro- and macro-nutrient malabsorptive factors, mechanical unloading and changes in molecules partaking in the crosstalk between adipose tissue, bone and muscle may play a determining role. Given these circumstances, it is conceivable that bone health should be adequately investigated in candidates to bariatric surgery through bone-specific work-up and dedicated postsurgical follow-up. Specific protocols of nutrients supplementation, motor activity, structured rehabilitative programs and, when needed, targeted therapeutic strategies should be deemed as an integral part of post-bariatric surgery clinical support.

Keywords: bariatric surgery; bone loss; bone mineral density; bone turnover; fracture risk; rehabilitation.

Figure 1

Similarities and homologies between adipose tissue and bone.

Figure 2

Visual graph of changes over time of bone turnover markers levels after bariatric surgery procedures (RYGB and SG). Data extracted from the references (116, 118,120).

Figure 3

Prospective 5-year observational study of cortical porosity at the distal radius and tibia after RYGB in 21 adults with severe obesity. Declines in cortical and trabecular microarchitecture led to decreases in estimated failure load of -20% and -13% at the radius and tibia (46).

Figure 4

Summary of the two hypothesized mechanisms to explain the susceptibility of obese patients to bone fractures. The negative effects of adiposity on bone fragility are reported in the upper box: obesity is associated with alterations in adipokines and cytokines levels, deregulation of peptides and hormones related to bone metabolism, and dyslipidaemia (112, 146). All these factors contribute to alter bone resorption and formation, by acting directly on osteoclast and osteoblast or indirectly through different molecular pathways. The factors that influence the risk of falling in obesity are reported in the lower box: the mechanistic links between falls and obesity include chronic health conditions, medication use and sedentary behaviour, which lead to a reduction in muscle strength and agility (147). Moreover, biomechanical alterations including poor muscle quality, impaired postural control and osteoarthritis, may reduce postural stability and muscle performances, thus inducing walking deficit and functional disability (–150).

Figure 5

Putative mechanisms linking post-bariatric surgery weight loss to changes in bone cells.