Kate Johnson

May 23, 2011

May 23, 2011 (Montreal, Quebec) — In obese individuals, the distribution of adipose tissue both on the body and in the liver and skeletal muscle is an important predictor of insulin sensitivity, according to a study presented here at the International Society for Magnetic Resonance in Medicine 2011 Annual Meeting.

"From these findings, BMI alone seems to be not a good measure for obesity in terms of metabolic alterations," said Jürgen Machann, Dipl. Phys., from the Section on Experimental Radiology at University Hospital in Tübingen, Germany. "There seems to be a benign form of adiposity. The lower the fat on the body, the better for the metabolic status, expressed as insulin sensitivity," he said.

The study included 144 obese volunteers, of whom 90 were female and 54 male, with an average age of 47 and 44 years, respectively. All subjects were at increased risk of developing type 2 diabetes and had body mass indices (BMIs) of between 33 and 35 kg/m2.

Quantification of different adipose tissue compartments was performed using T1-weighted magnetic resonance imaging (MRI), whereas single-voxel spectroscopy was used to determine ectopic lipids in the liver and skeletal muscle.

Adipose tissue measurements included total adipose tissue; visceral adipose tissue; subcutaneous abdominal adipose tissue; adipose tissue of the lower extremities, measured from the feet to the head of the femur; and adipose tissue of the upper extremities, ranging from the head of the humerus to tips of the fingers.

Postprocessing was performed by a semiautomatic segmentation procedure. In total, between 100 and 120 images were generated per patient, which took approximately 20 minutes each, said Dr. Machann.

The subjects were divided into 2 groups based on those who were insulin sensitive or insulin resistant after an oral glucose tolerance test.

Despite no significant differences between the groups in terms of BMI, percentage of total adipose tissue (between 37% and 49%), or percentage of subcutaneous abdominal adipose tissue (between 14% and 20%), subjects who were insulin resistant had a higher percentage of visceral adipose tissue compared with insulin-sensitive subjects — a difference that just missed statistical significance (5.2% vs. 5.9%, P = .07) in males but was significant in females (3.3% vs.3.9%, P = .02), said Dr. Machann.

In contrast, insulin-sensitive subjects had a higher percentage of lower-extremity adipose tissue compared with insulin-resistant subjects (14% vs.12% [P = .04] in males and 20% vs. 18% [P = .002] in females).

The picture for upper body adipose tissue was less clear, with insulin-resistant females showing significantly higher percentages than insulin-resistant females but insulin-resistant males showing slightly lower percentages than males with insulin sensitivity.

Hepatic lipids are more than doubled in both insulin-resistant males and females compared with insulin-sensitive subjects (P < .001 for both), Dr. Machann reported.

"Benign" adiposity seems to be characterized by decreased levels of hepatic lipids and increased amounts of adipose tissue in the lower extremities, the German investigator concluded.

"This reflects the well-known apple and pear shape, but we have to recognize that there are even male pears and female apples," he said.

The findings underscore the valuable role that imaging could play in daily clinical practice, said Scott Reeder, MD, PhD, comoderator of the session, associate professor, and section chief of MRI and cardiovascular imaging at the University of Wisconsin School of Medicine and Public Health in Madison.

"I think that's a reasonable thing we should be looking at in the future as new techniques come out that can do this rapidly," he said in an interview.

"If there's some concern based on a patient's weight or BMI you could go get a more accurate answer with imaging," Dr. Reeder said. Previously, it would take many hours to segment all those areas and to measure the visceral vs subcutaneous fat, but now there's more automated ways of doing this. So, for example, with just a couple of minutes of scanning and then automated segmentation you can get the answer right away, and that really brings the cost down. It's fast, it's noninvasive, and it's inexpensive."

Dr. Machann and Dr. Reed have disclosed no relevant financial relationships.

International Society for Magnetic Resonance in Medicine (ISMRM) 2011 Annual Meeting: Abstract 739. Presented May 13, 2011

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