Background: Definitions of metabolically healthy obesity (M-H-O) vary, leading to inconclusive results on long-term health outcomes. In addition, the M-H-O phenotype may not be a stable condition.

Objectives: To analyze the prevalence and time course of M-H-O and identifying metabolic factors that may be responsible for changes in phenotype. In addition, to assess the association between the presence of M-H-O and cardiovascular events, incident diabetes, overall and cardiovascular mortality.

Methods: Data of over 4,000 individuals recruited between 2000 and 2003 and followed up until the second visit in 2011-2015 for the prospective Heinz Nixdorf Recall cohort study were analyzed. Obesity was defined by body mass index (BMI; ≥30 kg/m²) and waist circumference (men: >102 cm, women >88 cm). Subjects were defined as M-H-O if they met 0 or ≤ 1 of the metabolic syndrome criteria according to the definition of the National Cholesterol Education Program, Adult Treatment Panel III.

Results: The prevalence of M-H-O was low by all definitions (1.5-14.3%) and more than 60% of M-H-O subjects were women. Over a 15-year follow-up period, 50-80% of those initially defined as M-H-O did not remain metabolically healthy. Hypertension or a combination of elevated blood glucose levels and hypertension were the main reasons for not maintaining the M-H-O status. Compared with metabolically unhealthy obese subjects M-H-O individuals were better positioned with regard to type 2 diabetes (adjusted odds ratios (OR) for all definitions: 0.53-0.79) and overall mortality (adjusted hazard rations (HR) for all definitions: 0.50-0.88). Few conclusions could be drawn for the occurrence of cardiovascular events (OR for all definitions: 0.47-1.09) and cardiovascular mortality (HR for all definitions: 0.70-1.74) due to the imprecise estimates.

Conclusion: The prevalence of M-H-O was low and this phenotype relatively unstable. M-H-O individuals had a lower chance of developing type 2 diabetes and lower all-cause mortality event rates.