Fran Lowry

November 30, 2012

CHICAGO — Visceral or deep belly fat might be a risk factor for bone loss and decreased bone strength in men, according to a study presented here at the Radiological Society of North America 98th Scientific Assembly and Annual Meeting.

Dr. Miriam Bredella

In the past, osteoporosis was thought to affect mainly women, and obesity was thought to protect against the disease, lead author Miriam Bredella, MD, from the Massachusetts General Hospital and Harvard Medical School in Boston, told Medscape Medical News.

"But then, a large multicenter study, called the Osteoporotic Fractures in Men Study, which was designed to determine risk factors for osteoporosis, showed that obesity in men was associated with increased fracture risk," Dr. Bredella said.

To date, no studies have looked at the effects of different abdominal fat depots on bone microarchitecture and strength in obese men, so Dr. Bredella and her group decided to.

They studied 35 obese but otherwise healthy young men (mean age, 33.8 years; mean body mass index [BMI], 36.5 kg/m²).

The men underwent a quantitative computed tomography (CT) scan of the abdomen and thigh to assess fat and muscle mass, as well as very-high-resolution CT of the forearm to measure the microarchitecture of the bone.

"High-resolution CT allows the performance of finite element analysis (FEA), a technique that is frequently used in mechanical engineering to determine the true strength of construction materials in the design of bridges or airplanes," Dr. Bredella explained.

FEA "can determine where a structure will bend or break, and the amount of force necessary to make a material break," she said. "We can now use FEA in conjunction with the high-resolution CT images to determine bone strength and fracture risk."

The FEA analysis showed that the men with more visceral and total abdominal fat had a lower failure load and less stiffness — 2 measures of bone strength — than men with less visceral and abdominal fat (< .05), even though their BMIs were similar.

Visceral abdominal fat was inversely associated with estimated failure load (r = –0.42; P = .01), as was total abdominal fat (r = –0.39; P = .03).

Visceral abdominal fat was also inversely associated with stiffness (r = –0.45; P = .008) and total abdominal fat (r = –0.42; P = .02).

There was no association between age, BMI, abdominal or thigh subcutaneous fat, and bone mechanical properties.

Thigh muscle, however, correlated positively with failure load (r = 0.39; = .02) and stiffness (r = 0.34; = .05).

"Obesity in men does not protect against osteoporosis, as previously thought. And visceral fat is detrimental to bone strength," Dr. Bredella emphasized.

Where We Gain Weight is Out of Our Control

"Obese men should be aware that excess visceral fat is not only a risk factor for heart disease and diabetes, but also a risk factor for bone loss. Unfortunately, we cannot control where we gain weight, whether it is in the deep abdominal cavity or superficial. Therefore, it's very important to maintain a healthy body weight," she said.

The best way to prevent bone degradation is to eat a healthy diet that contains adequate amounts of calcium and vitamin D, Dr. Bredella added.

Weight-bearing exercise (such as walking or climbing stairs) and resistance training (such as weight lifting) are ideal for preventing bone loss, she continued.

"Strength training can also prevent falls, which are the most common cause of hip and wrist fractures," she said.

Dr. Thomas Link

The finding that excess weight is not protective against bone loss is very important, said Thomas Link, MD, PhD, chief of the musculoskeletal imaging section in the Department of Radiology and Biomedical Imaging at the University of California, San Francisco, who was asked by Medscape Medical News to comment on this study.

"We've always thought that people with a high BMI...would have really good bones because they have constant loading on their bones. It turns out that this isn't correct," Dr. Link said.

It could be that patients who have a lot of fat just underneath the skin are not at risk for osteoporosis or weakened bones, but for those with fat surrounding their organs, the danger is clear, he noted.

"As a radiologist, I see this often. We take a CT and it shows that the person has giant masses of subcutaneous fat but not much fat around their organs. We have other patients who have a tiny bit of subcutaneous fat, but have huge masses of fat around the bowel, liver, and aorta. We've learned that this pattern is a risk factor for atherosclerosis and diabetes, and is definitely a sign of bad health," he said.

"People who are found to have a lot of visceral fat should be tested for bone mineral density, especially if they are older than 50 or 60. I don't advocate testing younger people, however," Dr. Link said.

Dr. Bredella has disclosed no relevant financial relationships. Dr. Link reports a financial relationship with General Electric.

Radiological Society of North America (RSNA) 98th Scientific Assembly and Annual Meeting: Abstract SSM12-02. Presented November 28, 2012.