Metabolically benign obesity: its identification and characterization
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Measurements of total body, visceral, and subcutaneous fat (using magnetic resonance (MR) tomography) and of liver and skeletal muscle fat (using proton MR spectroscopy) were conducted in 314 healthy subjects in order to better characterize the so-called “metabolically normal obesity”. Insulin sensitivity was estimated based on oral glucose tolerance testing. Subjects were divided into four groups: normal weight, overweight, obese-insulin sensitive (IS) and obese-insulin resistant (IR). Total body and visceral fat were significantly higher in the overweight and obese groups compared with the normal-weight group, whereas no difference was observed between the obese groups. In contrast, ectopic fat in skeletal muscle and in liver and intima-media thickness of the common carotid artery were lower whilst insulin sensitivity was higher in the obese-IS group as compared to the obese-IR group. Insulin sensitivity and intima-media thickness of the common carotid artery were not significantly different in the obese-IS group compared to the normal-weight group. A metabolically benign obesity that is not accompanied by insulin resistance and early atherosclerosis does exist in humans. Differences in liver ectopic fat, rather than in visceral fat, may partly underlie such a benign obesity phenotype.
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