Cutting Calories Alone May Lead to Osteoporosis
Dieters take note: You really should exercise, too. Many dieters don't realize it, but losing weight by restricting calories usually means losing bone density as well–and that can lead to osteoporosis. But a new study published in the December issue of the Archives of Internal Medicine found that exercise can stave off the bone loss associated with losing weight.
"If you're trying to lose weight, you really want to combine caloric restriction and exercise," says study author Dennis Villareal, an associate professor of medicine in the gerontology division at Washington University School of Medicine. That's particularly true for women who are at high risk of developing osteoporosis, such as those who have been through menopause or who have a family history of the disease.
Villareal divided his 48 study participants into groups of dieters, exercisers, and a control group. The diet group cut caloric intake about 20 percent by changing eating habits; the exercise group worked with trainers to burn an equivalent amount of energy; and the control group did neither. After a year, the dieters had lost a significant amount of bone mass, 2.2 percent, while the exercise group had not. The authors theorize that the strings of muscle that pull on bones during exercise stimulate the production of new bone, while dieting alone does not.
The study is part of a larger project called CALERIE coordinated by the Duke Clinical Research Institute that is trying to tease out the long-term health effects of a low-calorie diet. Animal research indicates that adopting a low-calorie diet may slow the aging process considerably.
Lona Sandon, a registered dietitian and a spokesperson for the American Dietetic Association, agrees with Villareal's recommendation that dieters need to exercise. "If you just cut calories alone, you can do more harm than good," she says. Sandon recommends moderate exercise five or six times a week and that women at risk for osteoporosis make a special effort to get enough calcium and vitamin D. Sandon also notes that weight-bearing exercise such as running offers more protection against bone loss than non-weight-bearing exercise such as biking or swimming.
Though exercise showed a protective effect on bone health in this study, Villareal emphasizes that the results don't indicate that low-calorie diets are harmful over the long term. "It's important that caloric restriction not be seen as a bad thing, because it offers enormous benefits with respect to reducing disease risk and is effective for weight loss," says Villareal. "There is a real possibility that caloric restriction provides antiaging benefits that cannot be achieved through exercise alone."
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