Higher rates of diabetes, ASCVD, heart failure, death
The current population-based study included 381,363 U.K. Biobank participants who were followed up for a median 11.2 years. Overall, about 55% did not have obesity or metabolic abnormalities, 9% had metabolically healthy obesity, 20% were metabolically unhealthy but did not have obesity, and 16% had metabolically unhealthy obesity as defined by the investigators.
The investigators adjusted the data for several potential confounders, including age, sex, ethnicity, education, socioeconomic status, smoking status, physical activity, and dietary factors.
Compared with individuals without obesity or metabolic abnormalities, those with metabolically healthy obesity had significantly higher rates of incident diabetes (hazard ratio, 4.32), ASCVD (HR, 1.18), myocardial infarction (HR, 1.23), stroke (HR, 1.10), heart failure (HR, 1.76), respiratory diseases (HR, 1.28), and chronic obstructive pulmonary disease (HR, 1.19).
In general, rates of cardiovascular and respiratory outcomes were highest in metabolically unhealthy obesity, followed by those without obesity but with metabolic abnormalities and those with metabolically healthy obesity. However, for incident and fatal heart failure and incident respiratory diseases, those with metabolically healthy obesity had higher rates than did those without obesity but with metabolic abnormalities.
Compared with those without obesity or metabolic abnormalities, those with metabolically healthy obesity had significantly higher all-cause mortality rates (HR, 1.22). And, compared with those without obesity (regardless of metabolic status) at baseline, those with metabolically healthy obesity were significantly more likely to have diabetes (HR, 2.06), heart failure (HR, 1.6), and respiratory diseases (HR, 1.2), but not ASCVD. The association was also significant for all-cause and heart failure mortality (HR, 1.12 and 1.44, respectively), but not for other causes of death.
Progression from metabolically healthy to unhealthy is common
Among 8,512 participants for whom longitudinal data were available for a median of 4.4 years, half of those with metabolically healthy obesity remained in that category, 20% no longer had obesity, and more than a quarter transitioned to metabolically unhealthy obesity. Compared with those without obesity or metabolic abnormalities throughout, those who transitioned from metabolically healthy to metabolically unhealthy had significantly higher rates of incident ASCVD (HR, 2.46) and all-cause mortality (HR, 3.07).
But those who remained in the metabolically healthy obesity category throughout did not have significantly increased risks for the adverse outcomes measured.
Ms. Zhou and colleagues noted that the data demonstrate heterogeneity among people with obesity, which offers the potential to stratify risk based on prognosis. For example, “people with [metabolically unhealthy obesity] were at a higher risk of mortality and morbidity than everyone else, and thus they should be prioritized for intervention.”
However, they add, “Obesity is associated with a wide range of diseases, and using a single label or categorical risk algorithm is unlikely to be effective compared with prediction algorithms based on disease-specific and continuous risk markers.”
Ms. Zhou has no disclosures. One coauthor has relationships with numerous pharmaceutical companies; the rest have none. Dr. Freedhoff has served as a director, officer, partner, employee, adviser, consultant, or trustee for the Bariatric Medical Institute and Constant Health. He is a speaker or a member of a speakers bureau for Obesity Canada and Novo Nordisk, received research grant from Novo Nordisk, and received income of at least $250 from WebMD, CTV, and Random House. Dr/ Schulze has received grants from German Federal Ministry of Education and Research.