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3 December 2010

Belly fat may weaken bones

One of the few possible advantages of carrying extra weight is being shot down

In the past, doctors had suggested that excess body fat, which is associated with heart disease, diabetes, and many other bodily harms, may protect against the bone disease osteoporosis.

But now, a study finds that even this may be misleading. In fact, deep belly fat may contribute to osteoporosis, say scientists whose research will be presented at the Radiological Society of North America.

That's because the fat cells most likely produce substances, not yet understood, that lead to bone disease in addition to heart disease and diabetes, said Dr. Miriam Bredella of Harvard Medical School and Massachusetts General Hospital, where the study was conducted.

Bredella and colleagues looked at 50 premenopausal women and examined their fat using computerized tomography (CT), which can distinguish between compartments of fat. Bredella said the human body has two categories of fat: superficial fat, which lies under the skin, and visceral fat, which surrounds organs. The first type of fat has been shown to have benefits against diabetes and heart disease when distributed around the hips.

It's the second kind of fat, the deep belly fat, that is bad for bones, she said. The study found that this fat was associated with lower bone mineral density, a measure of bone strength.

Most other studies on fat and osteoporosis have looked at weight or body mass index (BMI), which do not reflect this distribution of fat, she said.

And there's no way to know where the fat goes when you gain weight, as it's largely determined by genetics, she said.

The researchers also used a new technique to look at bone marrow fat, or fat within bones, which also appears to make the bones weaker. Women with deep tummy fat also had more fat within their bones, Bredella said.

On the other hand, women with anorexia have also been known to be at increased risk of osteoporosis. The bottom line is that you should strive for a normal weight, because the extremes of too much or too little fat are both bad for bones, Bredella said.

The research is being presented for the first time at the conference, and has not yet appeared in a peer-reviewed journal. Further work should be done to confirm the results.

A future study will look at the relationship between deep belly fat and osteoporosis among men, Bredella said.

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