Bypass Surgery Reduces Micronutrients Related to Bone Metabolism in Obese Patients

Roux-en-Y gastric bypass (RYGB) worsens the inadequacy of micronutrients related to bone metabolism and is associated with secondary hyperparathyroidism and low bone mineral density values, particularly in adolescent patients, according to study results published in Obesity Surgery.

Nutritional deficiencies are common in obese individuals, and bariatric surgery can aggravate this condition, especially following procedures that involve malabsorption such as RYGB. Adolescence is an important time for the formation of bone tissue and skeletal development, and bypass surgery can contribute to alterations of bone metabolism. The goal of the current study was to evaluate and compare the bone metabolism in adolescents and adults prior to RYGB and for 12 months after surgery.

The cohort included 60 obese adolescents (mean age, 17.1 years) and 60 adults (mean age, 39.4 years) who were evaluated 30 days before RYGB and 6 and 12 months postsurgery. The researchers assessed sun exposure and serum concentrations of 25-hydroxyvitamin D (25[OH]D), calcium, phosphorous, magnesium, zinc, alkaline phosphatase, and parathyroid hormone. Bone mineral density was measured by dual-energy X-ray absorptiometry.

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Before surgery, no significant differences were observed between the 2 groups for 25(OH)D levels (adolescents, 21.87 + 7.52 ng/mL; adults, 21.73 + 7.60 ng/mL, P =.94) or sun exposure (adolescents, 17.1 ± 2.0 min/day; adults, 13.2 ± 5.2 min/day; P =.85). The adolescent group had a higher incidence of inadequate calcium, phosphorous, and zinc before surgery compared with the adult cohort and experienced a significant decrease in 25(OH)D (P <.01) and magnesium (P <.01) levels between 6 and 12 months after surgery. Similarly, the adult cohort also experienced a drop in serum zinc levels from before surgery to 6 months postsurgery and 12 months postsurgery (6 months, P <.01; 12 months, P <.01). Both cohorts had a significant increase in parathyroid hormone level from 6 to 12 months postsurgery (adolescent cohort, P =.04; adult cohort, P =.02) and when comparing levels before surgery with 1 year postsurgery (P <.01 for both). In the adult population, 40.4% of patients with osteopenia and osteoporosis had inadequate levels of 25(OH)D.

“This study draws attention to the metabolic alterations associated [with] longer exposure to obesity and indicates that the irreversible damaging effects this disease has on bone metabolism can occur in adolescence,” wrote the researchers, adding that additional “longitudinal studies evaluating the long-term effects of obesity on bone metabolism are needed and may provide a better understanding of the most effective control measures for a greater control of bone health in the presence of obesity.”

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Santos D, Lopes T, Jesus P, et al. Bone metabolism in adolescents and adults undergoing Roux-en-Y gastric bypass: a comparative study [published online February 28, 2019]. Obes Surg. doi:10.1007/s11695-019-03797-5