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Bone density

Skeletal examination should be part of bariatric care

Study find surgery can induce changes in hormones that can affect the central regulation of appetite and bone strength

Skeletal examinations should be a routine part of bariatric care, pre- and post-surgery, according to endocrinologists from the Garvan Institute of Medical Research, Sydney, Australia.

The researchers, who published the paper in the journal Obesity Reviews, claim that some types of bariatric surgery may cause bone loss, particularly when carried out on young people who have not yet reached their peak bone mass.

"Even though we don't yet understand all the mechanisms, we can see that the more radical the procedure, the greater the bone loss long-term," said Dr Malgorzata Brzozowska, who undertook the review as part of her PhD.

The review carried out a widespread analysis of current research into the complex interrelationships between fat, bone and nutritional restriction. In particular, the research examined surgery-induced changes in hormones that can affect the central regulation of appetite and bone strength.

These include the fat-derived hormones leptin and adiponectin; gut-derived hormones such as peptide YY, glucagon-like peptide 1 and ghrelin; and the hypothalamic regulator of energy balance, neuropeptide Y. However, while there is quite a lot of animal data concerning these hormones and their effects, human data are sparse.

"In many situations significant weight loss is associated with bone loss, with or without surgery,” said Brzozowska. “The more invasive types of surgery appear to heighten bone turnover and the associated bone loss. This is thought to be caused not only by rapid weight loss and absorption of fewer vital nutrients like vitamin D and calcium, but possibly also by changes in hormones released by fat and the gut, and their impact on the central nervous system.”

Associate professor, Jackie Center, believes that the findings are very important despite the widely held assumption that obese people are protected against bone fragility and fracture.

The researcher added that it has always been assumed that the heavier someone is, the denser their bones will be, because bones become strong when they carry a load. While that is true up to a certain point, the bones may not continue to become stronger in the very obese, who can also have low bone density and fracture.

"Increasing evidence suggests that in very obese people, the relationship between bone density and weight fails and that the excess fat is detrimental to bone,” said Center. "While there are many studies looking at weight loss and improvement in insulin sensitivity after bariatric surgery, very few look at what happens in bone.

They argued that as the number of bariatric operations increases, it is imperative to recognise mechanisms responsible for bariatric surgery-induced bone loss, with careful monitoring of bone health including long-term fracture incidence in patients undergoing these procedures.

"We are certainly not arguing against bariatric surgery, there is no doubt that it is an effective weapon against obesity and obesity-related diabetes,” said Center. “We just ask that doctors and patients take bone health into account. Bone mineral densitometry scans can be done and adequate calcium and vitamin D intake advised. For those patients at particular risk, additional monitoring may be advised and protective drugs considered."

There is some contradictory evidence that bariatric surgery reduces bone density, with one study suggesting that bariatric patients do not face an increased risk of bone fracture in the first two years after their operation. However, another study has reported that obese patients have a greater risk of complications following total knee replacement surgery, including post-surgical infections.

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