Editors' ChoiceObesity

Central obesity: Redefining normal BMI

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Science Translational Medicine  02 Dec 2015:
Vol. 7, Issue 316, pp. 316ec209
DOI: 10.1126/scitranslmed.aad8027

Obesity is linked to increased mortality. However, BMI (body mass index), the usual definition of obesity, may not actually be the best measure. Other metrics like WHR (waist-to-hip ratio), which measures central obesity (adipose tissue carried in the abdomen), may be better predictors of morbidity and mortality. Now Sahakyan et al. present data showing that normal-weight U.S. adults with central obesity have poorer long-term survival than those who have normal fat distribution, regardless of BMI.

These authors surveyed a nationally representative sample of 30,818 individuals. About half of these had a BMI greater than 18.5 and available WHR information. During a mean follow-up of 14.3 years, there were 3222 deaths; of these, 1404 were due to cardiovascular disease. A multivariable Cox proportional hazards analysis showed that WHR—but not BMI—was associated with a higher risk of mortality. Men of normal weight but with central obesity had a higher risk of death than men with a similar BMI and no central obesity, or men with any other combination of BMI and WHR (HR range 1.22 to 2.42), even when compared with obese men with central obesity. A similar but less pronounced pattern was seen in women, and mortality risk further increased with age in both sexes. Possible mechanisms linking WHR with increased mortality risk include visceral fat accumulation, decreased muscle mass, and decreased leg and buttock adiposity. The risk of central obesity was also apparent when only mortality from cardiovascular causes was considered (even beyond the influence of obesity-related cardiovascular risk factors).

Some caution should be exercised regarding these results because comorbidities were self-reported by the participants, and WHR was not measured with the commonly recommended technique (classification according to baseline parameters). Nonetheless, this study identifies people with normal-weight central obesity as a previously underappreciated target population for preventative strategies.

K. R. Sahakyan et al., Normal-weight central obesity: Implications for total and cardiovascular mortality. Ann. Intern. Med. 10.7326/M14-2525 (2015) [Abstract]

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