The "Metabolically-obese Normal-weight" Phenotype and Its Reversal by Calorie Restriction

The prevalence of overweight and obesity in Singapore is approximately half of that in the United States, yet the incidence of type 2 diabetes is similar, and is expected to double in the near future. This indicates that metabolic dysfunction, particularly insulin resistance, is widely prevalent even among individuals who are considered normal-weight or lean by conventional measures, i.e. body mass index (BMI) and percent body fat. These individuals are often referred to as "metabolically-obese normal-weight" (MONW), and have increased risk for cardiometabolic disease despite their normal BMI and total body fat values. The prevalence of the MONW phenotype varies across populations and differs markedly among different ethnicities. However, our understanding of the complex interactions between ethnicity, body composition, and metabolic dysfunction and its reversal remains rudimentary. Previous attempts to characterize the MONW phenotype are confounded by the small but significant differences in BMI or percent body fat between groups (even if all subjects were lean, within the "normal" range), with MONW subjects being always "fatter" than the corresponding control subjects. There are no published studies that prospectively recruited groups of metabolically healthy and unhealthy lean individuals matched on BMI and percent body fat. Furthermore, although weight loss improves body composition and many of the cardiometabolic abnormalities in most obese patients, little is known about the possible therapeutic effects of calorie restriction in MONW subjects. Accordingly, a better understanding of the MONW phenotype and the evaluation of therapeutic approaches for its reversal will have important implications for public health. By facilitating earlier identification of these subjects, who are more likely to go undiagnosed and thus less likely to be treated before clinically overt cardiometabolic disease develops, results from this study will allow for earlier and effective i