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Exercising for Weight Loss a Boon to Bones

Posted on: Monday, 11 December 2006, 18:00 CST

By CHRISTINE DELL'AMORE

Losing weight through exercise prevents the loss of bone density that occurs from just cutting calories to shed pounds, a new study has found.

This suggests you'd want to do diet and exercise together to have less harmful effects on the bone, said lead author Dr. Dennis Villareal, an associate professor of medicine at the Washington University School of Medicine in St. Louis.

The preliminary findings, published in the Archives of Internal Medicine, part of the Journal of the American Medical Association, followed 48 adults -- 30 women and 18 men -- for one year. Villareal and colleagues measured any changes in their hip and spine bone mineral density.

The participants, who averaged 57 years of age, could not be obese or smoke; they also had to have maintained a stable weight for three months prior to the study, and the women had to be post-menopausal. The women could be on hormone replacement therapy if they'd taken it for at least six months before enrolling in the study.

The subjects were randomly divided into three groups: 10 in a control group, 19 in a group who exercised an hour a day while eating the same number of calories, and 19 in a group who ate up to 20 percent fewer calories. The control group got information on healthy lifestyles if they requested it.

The participants were weighed at the study's start, and then five additional times in the course of the year. Researchers measured their bone mineral density every three months using an X-ray technique. They also took blood samples of the subjects in order to test for hormones and analyze bone tissue.

The calorie-cutting group lost an average of a little over 18 pounds, the exercise group shed almost 15 pounds on average, and the control group did not lose any weight.

The calorie group also lost 2.2 percent of their bone density in the hips, the bone most vulnerable to fractures in older adults. The group also lost 2.2 percent of bone mineral density in the spine -- where post-menopausal women usually get fractures -- and 2.1 percent at the top end of the femur.

Most of the adults in the United States are now overweight or obese, and doctors still prescribe low-calorie diets and exercise as the gold standard for slimming down. But previous research has shown people who restrict calories to lose weight suffer bone mineral density loss, the strongest predictor of fracture due to osteoporosis.

Being overweight has also been linked to lower rates of osteoporosis, a phenomenon not completely understood. This is also why past studies on weight loss and bone density were not as dependable, Villareal said: They were done in obese people, whose bone mineral density is already substantial.

The study was limited by its small amount of study participants, and the fact the X-ray technology used to measure the bone mineral density could not measure bone quality, which is another factor in a person's risk for fracture.

The study highlights the benefit of the triad of bone-building habits: eating calcium-rich foods or taking supplements, engaging in weight-bearing exercise and maintaining a stable hormone status, said Christine Gerbstadt, a registered dietician and a spokesperson for the American Dietetic Association.

Lifting weights pulls on the skeleton, stimulating new bone production.

The main point is that exercise is far more important than most people give it credit, Gerbstadt said.

Also worthy of note, she said, is that weight-bearing exercises beyond walking are invaluable to bone health. Doing bicep curls and lunges with weights -- even with a 16 oz. water bottle in each hand -- can improve bone density immensely.

And although it's often portrayed as a disease of women, osteoporosis can also strike men, and both sexes can show signs in their 30s.

The study is part of a wider research effort on the effects of calorie restriction; Villareal and colleagues are now moving on to the second phase of their research, which will look at whether cutting calories can slow the primary aging process.

Source: United Press International

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