By Megan Rauscher, Reuters Health  

December 11, 2006

Men and women who lose weight through caloric restriction, without exercise, also lose bone at the hip and spine, increasing their risk for the bone-thinning disease osteoporosis and fractures, a study shows. Adding regular exercise to a calorie-restricted diet helps shield the bones from the harmful effects of dieting. 

"Exercise protects against bone loss during voluntary weight loss," Dr. Dennis T. Villareal, who led the study, told Reuters Health. "Therefore, it would be important to combine calorie restriction and exercise to derive the benefits of weight loss and preserve bone." 

Villareal, from Washington University School of Medicine in St. Louis, and colleagues studied the effects of weight loss on bone loss in 30 women and 18 men whose average age was 57 years. The study subjects were overweight but not obese. 

For one year, 19 subjects stuck to a calorie-restricted diet; 19 ate their usual number of calories but engaged in regular exercise; and 10 in a comparison "control" group received healthy lifestyle tips only. All but two participants completed the yearlong study. 

At the end of the 12 months, the dieters lost an average of 18.1 pounds, while the exercisers lost 14.8 pounds and those in the control group had no significant change in their weight. 

As reported in the Archives of Internal Medicine, the dieters lost an average of 2.2 percent of bone density in the lower spine and at the hip. In contrast, there were no significant changes in bone mineral density in the exercise group or healthy lifestyle groups. 

The action of muscles pulling on bones during exercise is thought to produce "healthy" strain on the skeleton that stimulates the production of new bone, the investigators note. The current study supports this line of thought. 

"It's important that calorie restriction not be seen as a bad thing," Villareal said, "because it offers enormous benefits with respect to reducing disease risk and is effective for weight loss. Also, there is a real possibility that calorie restriction provides anti-aging benefits that cannot be achieved through exercise alone."

However, to maintain healthy bones, "exercise should be an important component of a weight loss program to offset adverse effects of calorie restriction on bone," the team concludes. 

SOURCE: Archives of Internal Medicine, December 11/25, 2006.