Men with high levels of body fat have lower bone density and may be more likely to break a bone than those with normal levels of body fat, according to a new study published in the Endocrine Society’s Journal of Clinical Endocrinology & Metabolism.

Most studies have shown positive or neutral effects of body fat mass—the weight of fat in your body—on bone health. Lean mass is the entire weight of your body, including organs, skin and bones, minus fat. Health care providers often assume people with higher body weight have high bone density and are at low risk of fracture, and these patients are less likely to be screened for osteoporosis.

“We found that higher fat mass was related to lower bone density, and these trends were stronger in men than women,” said Rajesh K. Jain, MD, of University of Chicago Medicine in Chicago, Ill. “Our research suggests that the effect of body weight depends on a person's makeup of lean and fat mass, and that high body weight alone is not a guarantee against osteoporosis.”

The researchers analyzed the bone mineral density and body composition data of 10,814 people under 60 years old from the National Health and Nutrition Examination Survey (NHANES) 2011-2018. They found a strong positive association between lean mass and bone mineral density in both men and women. Conversely, fat mass had a moderately negative association with bone mineral density, especially in men.

“Health care providers should consider osteoporosis screening for patients with high body weight, especially if they have other risk factors like older age, previous fracture, family history, or steroid use,” Jain said.

Tamara Vokes of University of Chicago Medicine is the co-author of the study.

The study received no external funding.

The manuscript, “Fat Mass Has Negative Effects on Bone, Especially in Men: A Cross-Sectional Analysis of NHANES 2011-2018,” was published online, ahead of print.