Another Study Challenges Notion of ‘Healthy Obese’
The findings are also a reminder not to overlook normal-weight individuals, since one in 10 had metabolic risk factors for CVD.
Even in the absence of metabolic abnormalities, people who are obese are at higher risk of cardiovascular disease than their normal-weight peers, according to a large, contemporary population-based study.
To put it succinctly, study author G. Neil Thomas, PhD (University of Birmingham, United Kingdom), said "metabolically healthy" obesity simply does not exist.
“It is important to remember that fat is not just an energy store, but an active organ like the heart. It acts to help control food intake and factors like inflammation that have been shown to cause heart disease. It should therefore be no surprise that if you have more of it there will be consequences,” Thomas said in an email to TCTMD.
In the September 19, 2017, issue of Journal of the American College of Cardiology, Thomas and colleagues, including lead author Rishi Caleyachetty, PhD (University of Birmingham, England), report that they also observed that one in 10 normal-weight people had one or more metabolic abnormalities such as hypertension, dyslipidemia, and dysglycemia.
This is important, the study authors note, since obesity is often the red flag for busy clinicians that prompts them to look for other health problems. In fact, the US Preventive Services Task Force currently recommends using overweight and obesity as the main criteria to screen adults for abnormal blood glucose as part of CVD risk assessment.
“Our data should be a reminder to these clinicians that normal-weight individuals can carry these risk factors, and that this is associated with increased heart disease, so they need to be vigilant,” Thomas noted.
More Proof That Obesity Is Not Benign
The data come from the electronic health records of 3.5 million British adults who were initially free from CVD and were divided into four body-size phenotypes: underweight (BMI < 18.5), normal weight (more than 18 but less than 25), overweight (more than 25 but less than 30) and obese (> 30). Approximately 15% were classified as "healthy obese" (ie, no metabolic abnormalities). This group was more likely to be younger, male, current smokers, and to have lower levels of income, education, and employment.
Over follow-up of approximately 5 years, individuals who were obese but had no metabolic abnormalities had a higher risk of coronary heart disease (adjusted HR 1.49; 95% CI 1.45-1.54), cerebrovascular disease (adjusted HR 1.07; 95% CI 1.04-1.11), and heart failure (adjusted HR 1.96; 95% CI 1.86-2.06) compared with normal-weight individuals with no metabolic abnormalities. Among subjects who were metabolically healthy but obese, diabetes developed in 5.6%, hyperlipidemia in 11.5%, and hypertension in 10.5% over the follow-up period. Of note, however, metabolically healthy normal-weight subjects also developed risk factors: 1.9% developed diabetes, 9.4% hyperlipidemia, and 7.2% hypertension.
Being underweight and having no metabolic abnormalities also increased the risk of cerebrovascular disease, heart failure, and peripheral vascular disease compared with being normal weight with no abnormalities.
Across all BMI categories, risk of coronary heart disease increased with increasing number of metabolic abnormalities.
Metabolic Risks Shouldn’t Be Dismissed
In an editorial accompanying the study, Jennifer W. Bea, PhD, and Nancy K. Sweitzer, MD, PhD (University of Arizona, Tucson, AZ), say the risk to normal-weight individuals if metabolic dysfunction is present is great enough to advocate for increased need for screening in the normal-weight population.
“Often, one to two metabolic risk factors in normal-weight individuals are dismissed as unimportant because they are of healthy weight; however, these data suggest that the normal-weight group is at similar risk compared with overweight, and at times, obese individuals, when metabolic abnormalities are present,” they write.
But Bea and Sweitzer also say BMI is “an imperfect proxy for fat, particularly visceral fat, which may vary with race/ethnicity, sex, and age.” They therefore suggest that future studies should focus on body composition instead.
To TCTMD, Thomas said while he agrees that it is not ideal and preference should be given to waist size, most general practitioners do not measure it and in obese patients it is actually not so easy to measure.
“On a population level though, if you have a large waist you will very likely have a high BMI,” he added. “It is therefore not the best measure, but can still clearly convey risk, as seen in our study, and should not be overlooked.”
Caleyachetty R, Thomas GN, Toulis KA, et al. Metabolically healthy obese and incident cardiovascular disease events among 3.5 million men and women. J Am Coll Cardiol. 2017;70:1429-1437.
Bea JW, Sweitzer NK. More appropriate cardiovascular risk screening through understanding complex phenotypes: mind the gap. J Am Coll Cardiol. 2017;70:1438-1440.
- Caleyachetty, Thomas, Bea, and Sweitzer report no relevant conflicts of interest.