Bone and gastric bypass surgery - Weight Loss - Roux-en-Y gastric bypass

Nutrition Research Newsletter, Feb, 2004

Obesity is associated with a reduced risk of osteoporosis, whereas moderate weight loss has been reported to reduce bone mineral density (BMD) and ultimately lead to an increased risk of fracture. When there is a more dramatic weight loss, such as in women who have undergone Roux-en-Y gastric bypass (RYGB) and other surgical procedures for the treatment of morbid obesity, there is an increased risk of low bone mass, metabolic bone disease and fracture.

Inadequate intake of calcium and/or vitamin D and intestinal calcium malabsorption has been reported after intestinal bypass and RYGB. It has also been hypothesized that they lead to elevated levels of serum parathyroid hormone (PTH), which could contribute to bone loss. There should be less malabsorption after RYGB than after intestinal bypass, so the authors hypothesized that dietary calcium (Ca) and vitamin D would have a beneficial effect on bone mass and metabolism in RYGB subjects. Therefore, the recent study examined bone mass and metabolism in women who had previously undergone Roux-en-Y gastric bypass (RYGB) and determined the effect of supplementation with Ca and vitamin D.

BMD and BMC (bone mineral content) of the femoral neck, lumbar spine and ultradistal radius of the forearm were examined in 44 RYGB women and compared with 65 age-and weight-matched controls. The women had undergone the surgery greater than or equal to three years ago. The RYGB women who presented with low bone mass were asked to participate in a 6-month Ca and vitamin D supplementation study and were compared with the unsupplemented control group. The women were supplemented with a total of 1.2 g Ca/day and 8 [micro]g vitamin D/day over six months. To improve compliance, subjects were interviewed twice per month to obtain 24-hr dietary recalls. Bone mass and turnover and serum parathyroid hormone (PTH) and 25-hydroxy vitaimn D were measured.

Bone mass did not differ between premenopausal women from RYGB and the control group, whereas postmenopausal RYGB women had higher BMD and BMC at the lumbar spine and lower BMC at the femoral neck. Before and after dietary supplementation, bone mass was similar and serum PTH and markers of bone resorption were higher in RYGB compared with the control women and did not change significantly after supplementation.

Postmenopausal RYGB women show evidence of secondary hyperparathyroidism, elevated bone resorption and patterns of bone loss similar to other subjects with hyperparathyroidism. The results show that this cannot be suppressed by elevating their dietary intake of Ca and vitamin D to recommended levels. This study raises questions about the mechanism leading to secondary hyperparathyroidism in RYGB subjects, and points to the need for elucidating whether greater than recommended levels of Ca and vitamin D can suppress PTH and bone resorption in this population.

Lisa R. Goode, Robert E. Brolin, Hasina A. Chowdhury, et al. Bone and gastric bypass surgery: effects of dietary calcium and vitamin D. Obestiy Research 12(1): 40-46 (January 2004) [Correspondence: Sue A. Shapses, 96 Lipman Drive, Rutgers University, New Brunswick, NJ 08901-8525. E-mail: Shapses@aesop.rutgers.edu.]