Normal-Weight Central Obesity More Deadly Than Just High BMI

Miriam E. Tucker

November 09, 2015

Central obesity in normal-weight people places them at greater risk of death than does overall overweight or obesity in people without the excess abdominal fat, a new study suggests.

The startling findings were published online November 9, 2015, in Annals of Internal Medicine by Karine R Sahakyan, MD, PhD, of the Mayo Clinic, Rochester, Minnesota, and colleagues.

Their analysis of an average 14 years' follow-up data from more than 15,000 participants in the Third National Health and Nutrition Examination Survey (1988–1994) reveals that people who had normal body mass indexes (BMIs 18.5–24.9 kg/m2) but who had central obesity (defined using World Health Organization criteria of waist/hip ratio 0.85 or greater in women and 0.90 or above in men) had worse long-term survival compared with participants with normal fat distribution, regardless of their BMI.

"I was anticipating that normal-weight central obesity would be a risk factor for mortality compared with those with normal BMI and no central obesity. [But] to see that these individuals had a risk higher than that of obese by BMI was a surprise," principal investigator Francisco Lopez-Jimenez, MD, director of preventive cardiology at Mayo Clinic, told Medscape Medical News.

This means, he said, that clinicians should be measuring central distribution of fat and determining waist/hip ratio as part of a general medical evaluation.

This advice is counter to the most recent (2013) obesity management guidelines of the American Heart Association (AHA), American College of Cardiology (ACC), and Obesity Society (TOS), which advise measuring waist (not hip) only in people who are obese or overweight by BMI, the authors note.

"Fat distribution is important to assess cardiovascular risk, even in those with normal BMI....Those with normal BMI may have a false sense of reassurance without knowing their fat distribution," Dr Lopez-Jimenez commented.

In an accompanying editorial, Paul Poirier, MD, PhD, of the Institut Universitaire de Cardiologie et de Pneumologie de Quebec, Université Laval, agrees.

"Although the utility of BMI has been borne out in epidemiologic studies, there are limitations to using BMI alone to assess adiposity in clinical practice. The numerator in the BMI calculation is total body weight and does not distinguish between lean and fat mass," he says.

"The long-term deleterious consequences of excess adiposity are marked and important. These new data provide evidence that clinicians should look beyond BMI."

Normal Weight, Central Fat

The study included 7249 men and 7935 women. Of the total 15,184, 40% had normal BMI, 35% were overweight (25–29.9 kg/m2), and 25% were obese (>30.0 kg/m2). At the same time, more than two-thirds (70%) met the WHO waist/hip ratio criteria for central obesity.

Of the group with normal BMI, 11% of the men and 3% of the women had a waist/hip ratio above 1.0. Among those who met the overweight criteria by BMI alone, 37% of the men and 12% of the women had that degree of central adiposity, as did 63% of the men and 14% of the women who were obese by BMI criteria only.

Over a mean 14 years of follow-up, there were a total 3222 deaths, of which 1404 were due to cardiovascular disease.

After adjustment for multiple confounders, the waist/hip ratio was highly associated with mortality, whereas BMI was not.

Men with normal-weight central obesity had an 87% higher total mortality risk than did those with similar BMI but no central obesity (hazard ratio [HR], 1.87), and those men had more than twice the mortality risk compared with men who were overweight or obese but did not have central obesity.

Among the women, those with normal-weight central obesity had a 48% higher total mortality risk than did those with similar BMI but no central obesity, a 40% greater risk than those who were overweight without central obesity, and a 32% elevated risk compared with BMI-defined obese women without central obesity.

Sensitivity analyses excluding deaths within 6 months and looking at just cardiovascular mortality produced similar results: both men and women with normal-weight central obesity had a higher cardiovascular mortality risk than did those with similar BMI without central obesity (HR 1.78 for men, 2.25 for women).

Measurement of Waist and Hip Matters

Dr Lopez-Jimenez told Medscape Medical News, "Most experts have disregarded the measurement of waist, or waist-to-hip ratio, because of the claim that people with central obesity are obese by BMI anyway, so why bother measuring two additional things? Our study proves that assumption wrong."

While measuring the hip and waist is "very easy," he acknowledged that reducing central adiposity may be more difficult than just reducing overall body weight.

"An abnormal waist-to-hip ratio may require more effort to improve the diet and increase physical activity and lose fat tissue," he said, adding that recommending strength training to improve muscle mass may help.

Dr Poirier pointed out that in the 2013 AHA/ACC/TOS recommendations, lack of available data was cited as the reason for not recommending waist/hip ratio assessment, but that others have advocated for the use of both BMI and waist circumference to assess adiposity.

Moreover, Dr Poirier writes, "It was proposed that persons with an elevated BMI or a disproportionally high [waist circumference] for a given BMI should have other cardiometabolic risk factors evaluated for further risk stratification. These new data from Sahakyan and colleagues support this approach."

Dr Sahakyan received study support from the National Institutes of Health. Dr Lopez-Jimenez has no relevant financial relationships. Disclosures for the coauthors are listed in the paper. Dr Poirier has no relevant financial relationships.

Ann Intern Med. Published online November 9, 2015. Abstract, Editorial

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