True fractional calcium absorption is decreased after Roux-en-Y gastric bypass surgery

Abstract

Objective: Roux-en-Y gastric bypass (RYGB) is considered to be the gold standard alternative treatment for severe obesity. Weight loss after RYGB results primarily from decreased food intake. Inadequate calcium (Ca) intake and metabolic bone disease can occur after gastric bypass. To our knowledge, whether malabsorption of Ca contributes to an altered Ca metabolism in the RYGB patient has not been addressed previously.

Research methods and procedures: We recruited 25 extremely obese women in order to study true fractional Ca absorption (TFCA) before and 6 months after RYGB surgery, using a dual stable isotope method ((42)Ca and (43)Ca) and test load of Ca (200 mg). Hormones regulating Ca absorption and markers of bone turnover were also measured.

Results: In 21 women (BMI 52.7 +/- 8.3 kg/m(2), age 43.9 +/- 10.4 years) who successfully completed the study, TFCA decreased from 0.36 +/- 0.08 to 0.24 +/- 0.09 (p < 0.001) after RYGB. Bone turnover markers increased significantly (p < 0.01). TFCA correlated with estradiol levels (r = 0.512, p < 0.02) and tended to correlate with 1,25 (OH)(2)D (r = 0.427, p < 0.06) at final measurement. Stepwise linear regression indicated that estradiol explained 62% of the variance for TFCA at 6 months post-surgery (p < 0.01).

Discussion: TFCA decreases (0.12 +/- 0.08) after RYGB surgery but remains within normal range. Although only some patients were estimated to have low Ca absorption after surgery, all of the patients showed a dramatic increase in markers of bone resorption. The alteration in Ca metabolism after RYGB-induced weight loss appears to be regulated primarily by estradiol levels and might ultimately affect bone mass.

Figures

Figure 1

(A) Individual changes (solid lines) in TFCA and (B) total estimated calcium absorbed (mg/d) from baseline to final measurement 6 months after RYGB surgery in 21 extremely obese women. Dashed line and diamonds represent group means at baseline and 6 months after RYGB surgery.

Figure 2

Changes (%) in bone resorption (sNTx) and bone formation (osteocalcin) markers from baseline to final measurement 6 months after RYGB surgery (p < 0.0001) in 21 extremely obese women. Diamonds and solid line represent sNTx; open squares and dashed line represent osteocalcin.

Figure 3

Association between TFCA and estradiol levels (r = 0.512, p < 0.02) 6 months after RYGB surgery in 21 extremely obese women.