Metabolically healthy obesity and risk of mortality: does the definition of metabolic health matter?

Abstract

Objective: To assess the association of a "metabolically healthy obese" phenotype with mortality using five definitions of metabolic health.

Research design and methods: Adults (n = 5,269; 71.7% men) aged 39-62 years in 1991 through 1993 provided data on BMI and metabolic health, defined using data from the Adult Treatment Panel-III (ATP-III); criteria from two studies; and the Matsuda and homeostasis model assessment (HOMA) indices. Cross-classification of BMI categories and metabolic status (healthy/unhealthy) created six groups. Cox proportional hazards regression models were used to analyze associations with all-cause and cardiovascular disease (CVD) mortality during a median follow-up of 17.7 years.

Results: A total of 638 individuals (12.1% of the cohort) were obese, of whom 9-41% were metabolically healthy, depending on the definition. Regardless of the definition, compared with metabolically healthy, normal-weight individuals, both the metabolically healthy obese (hazard ratios [HRs] ranged from 1.81 [95% CI 1.16-2.84] for ATP-III to 2.30 [1.13-4.70] for the Matsuda index) and the metabolically abnormal obese (HRs ranged from 1.57 [1.08-2.28] for the Matsuda index to 2.05 [1.44-2.92] for criteria defined in a separate study) had an increased risk of mortality. The only exception was the lack of excess risk using the HOMA criterion for the metabolically healthy obese (1.08; 0.67-1.74). Among the obese, the risk of mortality did not vary as a function of metabolic health apart from when using the HOMA criterion (1.93; 1.15-3.22). Similar results were obtained for cardiovascular mortality.

Conclusions: For most definitions of metabolic health, both metabolically healthy and unhealthy obese patients carry an elevated risk of mortality.

Figure 1

Association of abnormal metabolic health status with all-cause mortality in analyses stratified by BMI categories. Analyses adjusted for age, sex, occupational position, physical activity, smoking, alcohol, fruit and vegetable consumption, marital status, and ethnicity. (A high-quality color representation of this figure is available in the online issue.)