Are metabolically normal but obese individuals at lower risk for all-cause mortality?

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.

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).

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.

Although a rare phenotype, obesity, even in the absence of overt metabolic aberrations, is associated with increased all-cause mortality risk.