Insulin-sensitive obesity in humans – a ‘favorable fat’ phenotype?

In most humans, obesity and insulin resistance coexist. However, a unique group of obese individuals, who exhibit better insulin sensitivity than expected for their adiposity, has been the focus of recent research interest. We critically examine cross-sectional and lifestyle intervention studies in obese humans classified as ‘insulin-sensitive’ versus ‘insulin-resistant’ and review the few longitudinal studies comparing rates of cardiovascular disease, type 2 diabetes and all-cause mortality in these groups of individuals. We suggest that reduced deposition of fat, particularly of bioactive lipid intermediates, in muscle and liver is potentially protective. We propose that dynamic interventional studies in insulin-sensitive obese humans may increase understanding of the metabolic factors that play a role in obesity-associated insulin resistance in humans.