“Healthy” obesity, defined as obesity in the absence of metabolic risk factor clustering, has been the subject of much debate since the concept rests on the assumption that it is a stable physiological state, instead of a transient phase of obesity-associated metabolic deterioration. A scarce number of studies have examined if this profile is generally maintained in adults long-term or if there is a natural transition over time to unhealthy obesity.

Research in the Journal of the American College of Cardiology evaluated data collected over more than twenty years on British government workers starting at baseline (1992/1994) and obesity and metabolic status after 5 year, 10 year, 15 year, and 20 year follow-up examinations. “Obese” was defined as body mass index (BMI) ≥30 kg/m2 and “metabolically healthy” was defined as having <2 of the following: high-density lipoprotein cholesterol level <1.03mmol/l (men) and <1.29mmol/l (women); blood pressure ≥130/85mmHg or use of antihypertensive medication; fasting plasma glucose level ≥5.6mmol/l or use of antidiabetic medication; triacylglycerol level ≥1.7mmol/l; and homeostatic model assessment of insulin resistance >2.87 (baseline 90th percentile value).

Of the 66 healthy obese adults at baseline, 31.8% were unhealthy obese after 5 years and 40.9%, 34.8%, and 51.5% were unhealthy obese after 10, 15, and 20 years, respectively. The proportion of healthy obese adults deemed healthy non-obese at follow-up was 6.1%, 4.5%, 6.1%, and 10.6% after 5, 10, 15, and 20 years, respectively. After adjusting for age, sex, and ethnicity, the prevalence of unhealthy obesity after five years was 11.80 times greater in baseline healthy obese adults vs. healthy non-obese adults. Healthy obese adults were almost eight times more likely to progress to unhealthy obesity after 20 years compared to healthy non-obese adults as well.

Given the longer, more-detailed follow-up of this study, the authors conclude that the natural course for most healthy obese individuals is progression to metabolic deterioration. Clinicians may wish to carefully monitor healthy obese patients for changes in metabolic measures and encourage healthy eating and positive lifestyle habits for long-term health.