Dieting women may lose bone mass that doesn’t return

Postmenopausal women who lose weight can also lose bone mass. But a study finds that regaining that weight doesn’t necessarily replace the lost bone.

The small, exploratory study included 23 overweight women who had been through menopause and were not taking any hormone therapy or drugs that might affect their bone metabolism. Women are at high risk for osteoporosis after menopause.

For six months, the women participated in a regular program of endurance exercise to encourage weight loss of about 9 to 11 pounds. After that, the women were followed for a year. They were tested for bone density at the beginning of the study as well as six and 18 months later. Almost 40% had osteoporosis at the beginning of the study.

On average, the women lost about 8.6 pounds of fat, and after 18 months -- a year after they stopped exercising -- they had gained back an average of 6.4 pounds, almost all of it fat.

During the six months, the women also lost bone density in their lumbar spines and hips, and there was no significant bone recovery after they regained the weight. The study authors noted that the bone loss may have been prevented or reduced had women done exercise that increased bone density, such as strength training (non-impact cardiovascular exercise typically doesn’t build bone mass). They authors also speculated about whether low bone mass in some overweight and obese people may be partially blamed on repeated diet-and-weight-gain cycles.

The study was published online recently in the journal Obesity.