Healthy With Obesity? The Latest Study Casts Doubt

Miriam E. Tucker

June 16, 2021

People with "metabolically healthy obesity" are actually not healthy, since they are at increased risk for several adverse cardiometabolic outcomes, compared with people without obesity and or adverse metabolic profiles, new research suggests.

The latest data on this controversial subject come from an analysis of nearly 400,000 people in the U.K. Biobank. Although the data also showed that metabolically healthy obesity poses less risk than "metabolically unhealthy" obesity, the risk of progression from healthy to unhealthy within 3-5 years was high.

"People with metabolically healthy obesity are not 'healthy' as they are at higher risk of atherosclerotic cardiovascular disease [ASCVD], heart failure, and respiratory diseases, compared with nonobese people with a normal metabolic profile. As such, weight management could be beneficial to all people with obesity irrespective of metabolic profile," Ziyi Zhou and colleagues wrote in their report, published June 10, 2021, in Diabetologia.

Moreover, they advised avoiding the term metabolically healthy obesity entirely in clinical medicine "as it is misleading, and different strategies for risk stratification should be explored."

In interviews, two experts provided somewhat different takes on the study and the overall subject.

Lifestyle Should Be Explored With Every Patient Regardless of Weight

Dr Yoni Freedhoff

Yoni Freedhoff, MD, medical director of the Bariatric Medical Institute, Ottawa, said "clinicians and patients need to be aware that obesity increases a person's risk of various medical problems, and in turn this might lead to more frequent screening. This increased screening might be analogous to that of a person with a strong familial history of cancer who of course we would never describe as being 'unhealthy' as a consequence of their increased risk."

In addition to screening, "lifestyle should be explored with every single patient regardless of their weight, and if a person's weight is not affecting their health or their quality of life, a clinician need only let the patient know that, were they to want to discuss weight management options in the future, that they’d be there for them," said Freedhoff.

'Metabolically Healthy Obesity' Has Had Many Definitions

Matthias Schulze, DrPH, head of molecular epidemiology at the German Institute of Human Nutrition, Potsdam, and professor at the University of Potsdam, pointed out that the way metabolically healthy obesity is defined and the outcomes assessed make a difference.

In the current study, the term is defined as having a body mass index of at least 30 kg/m2 and at least four of six metabolically healthy criteria: blood pressure, C-reactive protein, triacylglycerols, LDL cholesterol, HDL cholesterol, and hemoglobin A1c.

In May 2021, Schulze and associates reported in JAMA Network Open on a different definition that they found to identify individuals who do not have an increased risk of cardiovascular disease death and total mortality. Interestingly, they also used the U.K. Biobank as their validation cohort.

"We derived a new definition of metabolic health ... that is different from those used in [the current] article. Importantly, we included a measure of body fat distribution, waist-to-hip ratio. On the other side, we investigated only mortality outcomes and we can therefore not exclude the possibility that other outcomes may still be related. [For example], a higher diabetes risk may still be present among those we have defined as having metabolically healthy obesity."

Schulze also said that several previous studies and meta-analyses have suggested that "previous common definitions of metabolically healthy obesity do not identify a subgroup without risk, or being at risk comparable to normal-weight metabolically healthy. Thus, this study confirms this conclusion. [But] this doesn't rule out that there are better ways of defining subgroups."

Clinically, he said "given that we investigated only mortality, we cannot conclude that our 'metabolically healthy obesity' group doesn't require intervention."

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.

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."

Zhou has no disclosures. One coauthor has relationships with numerous pharmaceutical companies; the rest have none. 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. Schulze has received grants from German Federal Ministry of Education and Research.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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