Summary

Overweight and obesity are linked with an increased risk of diabetes and heart disease. But a study from Germany now reveals that much depends on how the fat is distributed around the body. People with less fat in the liver and skeletal muscles and with normal arteries do not show insulin resistance, which is an early sign of diabetes.

Introduction

Obesity is on the increase and so, too, is type 2 diabetes. But obesity is a complex condition and individuals differ in their susceptibility to diabetes. Abdominal fat, or visceral fat, is thought to comprise the main risk factor in being overweight, with the 'apple-shaped' person being more at risk of diabetes and heart disease than the 'pear-shaped' person. But fat is also deposited in the liver and in skeletal muscle. How do these deposits compare with abdominal fat as a risk factor?

What was done

Researchers at the University of Tübingen. Germany, used magnetic resonance imaging to gain a picture of the fat distribution in 314 adults aged 18 to 69. They also measured insulin resistance using an oral glucose tolerance test. The thickness of the walls of the carotid arteries, which serve the brain, was also measured.

What was found

The researchers divided the participants into four groups: normal weight, overweight, obese but still sensitive to insulin, obese with insulin resistance. All in the overweight and obese groups had more total body fat and visceral fat than those who had a normal weight. The differences came in the fat distribution. Those with insulin resistance had more fat within their skeletal muscles and their livers than did those obese participants without insulin resistance. They also had a thickening of the carotid arteries, which is a known sign of atherosclerosis. In normal and overweight people, visceral fat was a powerful predictor of insulin resistance, but not so in the obese group.

What this study means

The findings suggest that there could be a 'metabolically benign' form of obesity where people do not have as high a risk of diabetes and heart disease as previously supposed. Fat deposits in the liver and skeletal muscles seem to distinguish harmful from benign obesity but the reasons why this should be remain unclear. The study shows that obesity is a complex issue and there is still much we just do not understand.