What distinguishes adipose tissue of severely obese humans who are insulin sensitive and resistant?

PURPOSE OF REVIEW: Despite a strong correlation between obesity and insulin resistance, 25% of severely obese (BMI >40) individuals are insulin sensitive. In this review, we will examine the factors in adipose tissue that distinguish the two groups, as well as reasons for believing the insulin-sensitive group will be less disease prone. RECENT FINDINGS: Obesity has been linked to the metabolic syndrome with an increase in visceral (intra-abdominal) compared to subcutaneous fat. Recent studies in which adipose tissue of insulin-sensitive and insulin-resistant patients with severe obesity were compared indicate that the insulin-resistant group is also distinguished by increases in oxidative stress and decreases in AMP-activated protein kinase (AMPK) activity. In contrast, changes in the expression of genes for SIRT1, inflammatory cytokines, mitochondrial biogenesis and function, and the two α-isoforms of AMPK showed more depot variation. Studies of how these and other changes in adipose tissue respond to bariatric surgery are still in their infancy. SUMMARY: Available data suggest that increases in oxidative stress, decreases in AMPK activity and SIRT1 gene expression, depot-specific changes in inflammatory, mitochondrial and other genes distinguish adipose tissue of insulin resistant from insulin-sensitive individuals with severe obesity.