Written by Kurt A. Kennel, M.D., a Mayo Clinic endocrinologist
When thinking about how much we weigh, most of think in terms of how much fat and muscle tissue we have (or wish we had). However, bone density is an equally important part of what makes up our body composition. It turns out that both obesity and weight loss can have negative implications for bone health.
Although heavier people have more dense bones than thin and especially underweight people, they may have more fractures than normal weight persons. Beyond a BMI of about 30 kg/m2, the increasing force of falls due to higher body weight outpaces the increase in bone density due to higher weight. If even the bones are more dense, some of the metabolic disorders (e.g., diabetes mellitus) associated with obesity seem to alter the bone tissue making it weaker. Finally, most fractures occur due to falls. Deteriorating joint health and other negative aspects of obesity on balance may lead to more frequent falls.
Intentional weight loss is always good for the body, correct?
Unfortunately, losing weight is virtually always “bad to the bone.” Hormonal, nutritional, and mechanical factors as well as other incompletely understood mechanisms often lead to bone loss. The most aggressive weight loss treatments like bariatric surgery are associated with the greatest bone loss and a higher chance of fractures. Even weight loss plans which achieve modest weight loss through healthier diet and exercise can result in bone loss. Fortunately, the amount of bone loss while losing weight can be modified even if not usually avoidable. When reducing total calorie intake, maintaining generous protein intake and calcium with vitamin D supplementation has been shown to attenuate bone loss even after weight loss surgery. Including resistance exercise as part of a weight loss program can also limit bone loss. Use of medications (such as those used to treat osteoporosis) to prevent bone loss during weight loss is as yet unproven.
Overall, concerns regarding bone loss should not hinder attempts to improve overall health and wellness with weight loss. However, the approach to weight loss should take into account bone health especially in those who already have low bone density or osteoporosis. Ideally, gradual weight loss would be achieved with a program which included adequate protein, calcium and vitamin D intake and a comprehensive physical exercise plan. Assessment of bone health prior to weight loss may be appropriate for menopausal women and older men especially if more aggressive treatment for weight loss is considered.