Author	J.A. Bell
Author	M. Kivimaki
Author	M. Hamer
Author	S. Sabia
Abstract	Background: Obesity is a major threat to public health given its strong links with cardiometabolic morbidity and premature mortality. One-third of obese adults are metabolically healthy, but little is known about modifiable determinants of this state or its progression over time. Aims: To determine whether physical activity and sedentary behaviour distinguish healthy from unhealthy obesity, and whether healthy obese adults have increased risk for developing metabolic ill-health and type 2 diabetes. Methods: Data were drawn from up to 5427 men and women participating in the Whitehall II cohort study. Normal-weight, overweight, and obese adults were considered healthy if they had <2 of 5 metabolic risk factors (hypertension, low HDL-cholesterol, high triglycerides, high blood glucose, and insulin resistance). Associations of self-reported moderate-to-vigorous physical activity and leisure sitting time with prevalence and 15-year incidence of metabolic risk factor clustering were examined among healthy obese adults. Differences in accelerometer-assessed total physical activity were also examined between healthy and unhealthy obese groups. Metabolic risk factor incidence among initially healthy obese adults was described, and published risk estimates of incident type 2 diabetes were systematically searched and meta-analysed. Results: Neither high self-reported moderate-to-vigorous physical activity nor low self-reported leisure sitting was associated with health among obese adults. Higher total physical activity among healthy versus unhealthy obese adults was evident through accelerometer assessment only (p=0.002). After 20 years, 52% of initially healthy obese adults were unhealthy obese, with insulin resistance being most commonly incident. Meta-analyses of 8 studies indicated that healthy obese adults have 4.03 (95% CI=2.66-6.09) times greater risk of incident type 2 diabetes than healthy normal-weight adults. Conclusions: Higher physical activity rather than lower sedentary behaviour distinguishes healthy from unhealthy obesity. Healthy obesity is strongly linked with future insulin resistance and type 2 diabetes, suggesting that it is not a harmless condition.