Adipose tissue inflammation and insulin resistance: all obese humans are not created equal

In recent years, it has become widely accepted that obesity is characterized by a chronic low-grade inflammation of adipose tissue that predisposes affected individuals to insulin resistance, Type 2 diabetes and other disorders associated with the metabolic syndrome. On the other hand, a subset of obese individuals appears to be protected against insulin resistance and the disorders to which it predisposes. The comparison between such insulin-sensitive and insulin-resistant obese individuals offers a unique opportunity to identify key factors that either contribute to or prevent the development of insulin resistance in humans, without the confounding effect of a major difference in fat mass. In the previous issue of the Biochemical Journal, Barbarroja et al. reported that insulin-sensitive obese individuals show less inflammation in their visceral adipose tissue than a group of insulin-resistant subjects matched for BMI (body mass index). This finding reinforces the concept that inflammation in adipose tissue may be a cause of insulin resistance in most obese individuals, although it does not prove it. Further studies will be required for this purpose, as well as to identify the pathogenetic factors that determine whether or not adipose tissue of an obese individual becomes inflamed.