A new study reveals that people with “central obesity” — a medical term often used to describe excess belly fat — have higher mortality rates than overweight or obese people with higher BMIs but with more evenly distributed body fat.

The new obesity research findings suggest that waist-to-hip ratio, a measurement of body fat distribution, is an important predictor of cardiovascular health and related mortality. The study concludes that body mass index (BMI), while important in determining obesity status, is not a complete indicator of overall health risks. The research paper, entitled “Normal-Weight Central Obesity: Implications for Total and Cardiovascular Mortality,” was published in Annals of Internal Medicine.

Central obesity is defined as a waist-to-hip ratio, a reliable but infrequently used measure, of above 0.9 for men and 0.85 for women, according to the World Health Organization (WHO). Waist circumference is also used as an indicator for central obesity, with cutoffs of 94 cm (men) and 80 cm (women), according to both the WHO and the International Diabetes Foundation.

The study is an effort to examine the relationship between total and cardiovascular mortality risk associated with central obesity in different BMI groups, especially adults who fall into the normal values in the BMI spectrum. Researchers evaluated BMI and waist-to-hip ratio values from a population of 15,184 adults (52.3% women), age 18 to 90 years, and tracked the participants for 15 years to access heart disease and mortality.

The results, adjusted for confounding factors, show that people with healthy BMIs (between 18.5–25) and central obesity had the worst long-term survival, meaning that, for example, a man with a BMI of 22 and central obesity had a greater risk of mortality than a man with similar BMI but no central obesity — and twice the mortality risk of participants that were overweight or obese according to BMI values, but did not present central obesity. These results were observed in both genders. Normalization of the population study results according to age and BMI still showed that those with central obesity presented lower expected survival rates.

Researchers conclude that central obesity defined by waist-to-hip ratio is associated with higher mortality than BMI-defined obesity, especially in the absence of central fat distribution. The results suggest that, when evaluating potentially at-risk patients, clinicians should take into account central obesity measurements, even in patients who are not obese by BMI standards. Patients who are obese according to BMI standards, but not centrally obese, would benefit more from counseling on improvements in mobility and quality of life, instead of a focus on cardiovascular disease.

Dr. Paul Poirier, MD, commented on the study results in an accompanying editorial: “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. The long-term deleterious consequences of excess adiposity are marked and important. These new data provide evidence that clinicians should look beyond BMI.”