We know that we lose fat and muscle when we lose weight. What happens to bone when we lose weight? Does it matter what treatment strategy you use to lose weight? And, does any change in bone with weight loss translate to an increase in fracture risk?
As blogged previously, the relationship between obesity and bone health is complex to begin with. Some people with obesity may be at higher risk of fracture in some locations, particularly the lower leg and ankle. A recent review summarizes the current state of knowledge on what happens to bone health and fracture risk with weight loss.
The first important point is that bone density decreases with weight loss by any treatment modality, which makes sense, as the bones do not need to support as much weight. Changes in bone metabolism seem to start happening around 7% to 10% weight loss mark.
As regards dietary strategies of weight loss, there’s not much information available on changes in bone architecture, strength, nor fracture risk. The LOOK AHEAD study, which examined a dietary induced weight loss strategy in people with type 2 diabetes, found that the intervention group, who lost an average of 6% weight, had no statistically significant differences in total fracture rates compared to the usual care group, who lost an average 3.5% weight. However, the intervention group did have a 39% higher risk of hip, pelvis, upper arm, or shoulder fractures than the standard care group.
We also don’t yet know much about changes in bone health or fracture risk with obesity medications. Evidence of GLP-1 receptor agonist effect on bone is limited, and mostly comes from studies of lower doses in people with type 2 diabetes without much weight loss and a short follow-up time period (too short to evaluate changes in bone). Several systematic reviews and meta-analyses suggest no difference in fracture risk in people with diabetes compared with placebo or other diabetes medication. In the longer SELECT cardiovascular outcome trial of semaglutide 2.4mg (Wegovy), which had an average follow up time of 40 months, more fractures of the femur and pelvis were reported in female patients with semaglutide (1%) than placebo (0.2%), and in patients 75 or older, 2.4% of people in the semaglutide group had a femur or pelvis fracture vs 0.6% with placebo. Overall, we are really lacking on information on bone density and fracture risk with GLP1 obesity treatments, studied in people with obesity, and including the newer more efficacious GLP1-based medications like semaglutide 2.4mg and tirzepatide (Mounjaro/Zepbound).
Bone health and fracture outcomes have only really been well assessed after bariatric surgery. Bone density decreases as expected with the usually substantial reductions in weight that occur with bariatric surgery. There is an increased risk of fracture after bariatric surgery, particularly the surgeries that alter absorption of nutrients such as gastric bypass surgery and biliopancreatic diversion with duodenal switch. There are many factors that can contribute to increased fracture risk, including nutritional factors, calcium, vitamin D and protein intake, mechanical unloading (less weight for bones to carry), and the hormonal changes that are unique to each type of surgery. Increased risk of falls due to changes in body composition, excessive muscle loss (sarcopenia), hanging skin, or distribution of weight/balance may contribute. Change in gut bacteria and even bone marrow fat may even play a role. Although weight generally stabilizes 12 months after bariatric surgery, bone loss continues beyond this time, suggesting that there is more than just weight loss going on as a contributing factor. The magnitude of weight loss after bariatric surgery has not been found to be associated with higher fracture risk.
How do we minimize loss of bone while losing weight? General measures include ensuring adequate calcium and vitamin D intake, avoiding tobacco and minimizing alcohol, adequate protein intake, and a combination of weight-bearing and resistance activity. For anyone losing weight, screening for excessive weight loss and sarcopenia, and assessing fall risk, are important. Specifics of calcium, vitamin D, and protein depend on which weight loss strategy is being employed . Those having bariatric surgery will have specific recommendations that may be different from those losing weight with weight loss medication or lifestyle change alone. These recommendations even vary by type of surgery – check out the Canadian Obesity Guidelines on post bariatric surgery guidance. In some cases (including after bariatric surgery), assessment of fracture risk with bone density is recommended, and in some cases, osteoporosis treatment may be recommended. Whatever strategy of weight loss you are using, talk to you health care team to develop a plan that is right for you.
BOTTOM LINE: We know that substantial weight loss with any treatment approach reduces bone density. Data on the effect of weight management medication on bone health and fracture risk are sorely lacking. We also do not know what happens with weight cycling (repeated yo-yo weight loss and gain); this is an important area needing further investigation. Ensuring good nutrition, physical activity, and screening for excessive weight/muscle loss and fall risk are important in any weight management journey.
Disclaimer: I am/have been an investigator in clinical trials of semaglutide and tirzepatide. I receive honoraria as a continuing medical education speaker and consultant from the makers of semaglutide (Novo Nordisk) and tirzepatide (Eli Lilly).
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