Bariatric surgery such as gastric bypass and stomach banding leads not only to weight loss but also to bone loss. This negative side effect is "frequent" according to a review of eleven studies where the effects of weight loss surgery on bone status have been published. The frequency of this unwanted effect contrasts with the high number of stomach surgeries, from twenty up to a hundred, that are needed to prevent one premature death within five years.
When balancing the pros and cons of stomach bypass or banding, all possible complications have to be considered. Unfortunately, only little is known about bone loss. Those patients undergoing gastric banding fare a bit better than those with a Roux-en-Y bypass when it comes to bones. The bone loss is beginning early after surgery, long before a weight loss has occurred. Therefore, it has nothing to do with a weaker weight impact on the bones.
The mechanism is not yet well understood. What can be measured are certain substances in the blood that are known to remove mass from the bones on the one hand and to add new mass to the bones on the other hand. After weight loss surgery, the bone-removing substances prevail. It seems that most is known about the short-term effect of weight-loss surgery on bones. It would be very desirable to learn more about the long-term effects.
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