Stability of metabolically healthy obesity over 8 years: the English Longitudinal Study of Ageing

OBJECTIVE: Metabolically healthy obesity possibly reflects a transitional stage before the onset of metabolic dysfunction, but few studies have characterised this transition. We examined the behavioural and biological characteristics of healthy obese adults that progressed to an unhealthy state over 8 years follow-up.

METHODS: Participants were 2422 men and women (aged 63.3±7.7 years, 44.2% men) from the English Longitudinal Study of Ageing. Obesity was defined as BMI ≥30 kg/m(2). Based on blood pressure (BP), HDL-cholesterol, triglycerides, HbA1c and C-reactive protein (CRP) participants were classified as 'healthy' (0 or 1 metabolic abnormality) or 'unhealthy' (≥2 metabolic abnormalities).

RESULTS: Over 8 years follow-up, 44.5% of healthy obese subjects had transitioned into an unhealthy state, compared to only 16.6 and 26.2% of healthy normal-weight and overweight adults respectively. Compared with healthy obese adults who remained stable, those who progressed to an unhealthy state were more likely to have high BP (75.0% vs 37.0%, age- and sex-adjusted odds ratio (OR) 8.9, 95% CI 4.7-17.0), high CRP (53.7% vs 17.0%, OR=8.6, 95% CI 4.1-18.0), high HbA1c (46.3% vs 5.9%, OR=13.8, 95% CI 6.1-31.2) and high triglycerides (45.4% vs 11.9%, OR=5.9, 95% CI 2.9-12.0) at follow-up, with excess risk remaining independent of lifestyle factors including self-reported physical activity. Progression to an unhealthy state was also linked with significant gains in waist circumference (B=2.7, 95% CI, 0.5-4.9 cm).

CONCLUSION: These data show that a healthy obesity phenotype is relatively unstable. Transition to an unhealthy state is characterised by multiple biological changes that are not fully explained by lifestyle risk factors.