Are Metabolically Normal but Obese Individuals at Lower Risk for All-Cause Mortality?

OBJECTIVE: The clinical relevance of the metabolically normal but obese phenotype for mortality risk is unclear. This study examines the risk for all-cause mortality in metabolically normal and abnormal obese (MNOB and MAOB, respectively) individuals. RESEARCH DESIGN AND METHODS: The sample included 6,011 men and women from the Third National Health and Nutrition Examination Survey (NHANES III) with public-access mortality data linkage (follow-up = 8.7 +/- 0.2 years; 292 deaths). Metabolically abnormal was defined as insulin resistance (IR) or two or more metabolic syndrome (MetSyn) criteria (excluding waist). RESULTS: A total of 30% of obese subjects had IR, and 38.4% had two or more MetSyn factors, whereas only 6.0% (or 1.6% of the whole population) were free from both IR and all MetSyn factors. By MetSyn factors or IR alone, MNOB subjects (hazard ratio HR(MetSyn) 2.80 1.18-6.65; HR(IR) 2.58 1.00-6.65) and MAOB subjects (HR(MetSyn) 2.74 1.46-5.15; HR(IR) 3.09 1.55-6.15) had similar elevations in mortality risk compared with metabolically normal, normal weight subjects. CONCLUSIONS: Although a rare phenotype, obesity, even in the absence of overt metabolic aberrations, is associated with increased all-cause mortality risk.