They suggest that during weight loss through calorie-restricted diets, bones are being remodelled i.e. old bones are broken down and new ones formed, at a rapid rate. At the same time, bone density is decreases, causing increased fragility.
During the study, the team examined protein markers of bone breakdown and formation in 37 obese, middle-aged adults who lost 20 percent of their body weight through a severe calorie-restricted diet.
Protein markers, which are released during bone breakdown and formation, were used as indirect indicators of bone remodelling.
During a 3-month weight-loss programme, bone remodelling was elevated, and bone formation and breakdown were imbalanced as a result of a low energy intake.
After weight loss phase, bone remodelling remained elevated during the 9-month weight maintenance, but bone formation and breakdown appeared to be balanced.
"When people increased their calorie intake after weight loss, the bone remodelling markers did not respond and remained above what they were before weight loss," said Pam Hinton, associate professor of nutritional sciences in the MU College of Human Environmental Sciences.
"However unlike the weight loss phase, it appeared that bone breakdown and bone formation were balanced. Rapid rates of bone remodelling, regardless of the balance of breakdown and formation, can increase bone fragility," she added.
The study showed that a greater reduction in body weight led to a greater increase in bone breakdown.
"From this study alone, it is impossible to determine the consequences of accelerated bone remodeling during weight maintenance. Because bone strength adapts to match skeletal load, body weight is one of the strongest predictors of bone mass," said Pam.
"People planning on losing a significant amount of weight should consider incorporating high-impact weight-bearing physical activity into their exercise routine and consuming adequate calcium to improve bone health," she added.