Losing weight in middle age might mean losing not just unwanted fat, but also precious bone density, at least for women, a new study suggests.
Regardless of the types of foods or amount of calcium in their diets, middle-age women who lost a moderate amount of weight over a two-year period also lost more bone density than men or younger women.
Changes in bone density after moderate weight loss might be sex-specific and influenced by hormones, the study team wrote in the Journal of Clinical Endocrinology and Metabolism.
“Weight loss has been associated with beneficial effects on cardiovascular risk factors like diabetes. However, extremes of weight loss have been associated with bone loss, and according to some studies, increased risk of fracture,” said senior author Dr. Meryl LeBoff of Brigham and Women’s Hospital in Boston.
LeBoff’s team analyzed data gathered during a large weight-loss study in which 424 participants were randomly assigned to follow one of four low-calorie diets. (Two diets were considered to be high-protein, and two contained an average amount of protein.)
Participants were 30 to 70 years old and overweight or obese at the start of the study. About 60 percent were women.
Bone-density measurements of the spine and hip were taken at the outset, six months into the diets and again after two years, at which point 236 men and women had completed the study.
By the end of two years, men lost an average of
8 percent of their original body weight, and women lost an average of 6.4 percent.
With comparable amounts of weight loss, “the women lost bone density at the spine and the hip in the postmenopausal group and the men actually gained bone density at the spine and had a stable bone density of the hip,” LeBoff said.
Premenopausal women lost bone density only at the hip, the study team noted.
And among menopausal women, loss of abdominal fat — the kind linked with heart disease and diabetes risk — was particularly linked to bone loss.
Differences in bone loss also were tied to the amount of muscle — known as lean mass — a person lost.
Dr. Kathryn Diemer, director of the Bone Health Program at the Washington University School of Medicine in St. Louis, said the loss of bone density in all the dieters looked to be quite small, about a 1 to 2 percent decrease.
“So while statistically significant, in terms of fracture risk, it isn’t much,” said Diemer, who wasn’t involved in the study.