Gravitational loading not tied to bariatric surgery induced bone loss: Study

Mechanical unloading associated with weight loss might be one of the main causes of bariatric surgery (BS) induced bone loss. However, no study has tested this hypothesis through objectively measured accelerometry-derived gravitational loading.

A group of researchers from Portugal aimed to assess how gravitational loading changes following BS and how this correlates with bone mass losses.

The researchers assessed a total of 21 patients submitted to gastric bypass before, 1, 6 and 12 months after bariatric surgery (BS) for areal bone mineral density (BMD), calciotropic hormones, sclerostin, body composition and daily physical activity. Gravitational loading was determined as the sum of ground reaction forces assessed by the accelerometer which considered the interaction between weight and daily ambulation.

The results of the study are as follows:

• Mechanical stimuli promoted through the significant increase in steps number counterbalanced the gravitational loading decreases derived from the significant weight loss after bariatric surgery (BS). Gravitational loading volume decreased between pre-BS and 1-month post-BS, but remained stable between 6- and 12-months post-BS, despite decreases on hip, femoral neck and lumbar spine BMD. Serum sclerostin increased from pre-BS to 1-month post-BS, returning to pre-BS levels 6 months after surgery.
• Neither vitamin D nor parathyroid hormones were affected by BS. Weight variation was a predictor of BMD decreases at the total hip and femoral neck, whereas daily gravitational loading volume was not.
• Fat and lean mass changes were also predictors of BMD decrease at the total hip and femoral neck respectively.

Thus, the researchers concluded that gravitational loading only decreased during the first month after surgery remaining stable thereafter, and these changes do not seem to explain BS-induced bone loss. The association between weight and bone loss seems to result from other physiological aspects, fat and lean mass loss, rather than from a gravitational loading decrease.

Reference:

The effect of bariatric surgery on gravitational loading and its impact on bone mass by Diniz-Sousa F et. al. published in Bone.

https://doi.org/10.1016/j.bone.2021.116153