New Obesity Metric Uses Body Shape to Predict Risk of Death

Medscape | Two researchers have developed a new metric, called A Body Shape Index (ABSI), for determining how obesity can predict the risk of premature mortality, they report in a study published online today in PLos One.

Nir Y. Krakauer, PhD, assistant professor of civil engineering at City College of New York City, and Jesse C. Krakauer, MD, an endocrinologist with Middletown Medical in Middletown, New York, analyzed the records of 14,105 nonpregnant adults aged 18 years or older who were included in the National Health and Nutrition Examination Survey 1999-2004 and followed up for 5 years. During follow-up, 828 deaths were recorded.

The researchers developed the ABSI based on waist circumference (WC), adjusted for height and weight, where high ABSI indicates that WC is higher than average for a given height and weight and body volume is more centrally concentrated. ABSI is not correlated, however, with height, weight, or body mass index (BMI). Their formula is WC divided by BMI2/3height1/2.

Using linear regression methods and Cox proportional hazard modeling, the authors calculated that death rates increased with above-average ABSI by 33% per standard deviation (95% confidence interval [CI], 20% – 48%). They found that 22% (95% CI, 8% – 41%) of the study population’s mortality hazard was attributable to ABSI compared with 15% (95% CI, 3% – 30%) attributable to BMI and 15% (95% CI, 4% – 29%) attributable to WC.

The associations held up after adjusting for other death risk factors including smoking, diabetes, high blood pressure, and serum cholesterol levels, as well as for age, sex, BMI, and white and black ethnicities, but not for Mexican ethnicity. The ethnic difference suggests that more study is needed to determine the limits of ABSI’s utility, they write.

“ABSI clearly has distinct impacts on mortality compared to BMI and WC,” the researchers write.

“Applying ABSI along with BMI as a predictor variable separates the influence of the component of body shape measured by WC from that of body size,” they explain.

“[H]igh ABSI may correspond to a greater fraction of visceral (abdominal) fat compared to peripheral tissue.”

The World Health Organization ranks overweight and obesity as the fifth leading cause of death, behind high blood pressure, tobacco use, high blood glucose, and physical inactivity, and according to the organization, the prevalence of overweight and obesity is more than 50% of adult populations in high- and middle-income countries. The researchers cite National Institute of Health guidelines that put overweight and obesity as the second leading cause of preventable death in the United States, behind tobacco use.

In recent research, they write, WC has emerged as a complement to BMI for predicting obesity risk because BMI does not account for the difference between muscle and fat accumulation or for fat locations such as abdominal fat. However, using WC as a predictor of abdominal fat is limited because it is dependent on size (namely, height and weight) and correlates closely with BMI.

The researchers conclude, “[B]ody shape, as measured by ABSI, appears to be a substantial risk factor for premature mortality in the general population derivable from basic clinical measurements. ABSI expresses the excess risk from high WC in a convenient form that is complementary to BMI and to other known risk factors.”

In a journal news release, Dr. Nir Krakauer comments, “Measuring body dimensions is straightforward compared to most other medical tests, but it’s been challenging to link these with health. Our results give evidence that the power-law scaling of [WC], weight, and other body measurements can be used to develop body shape indices that point to added risk.”

The study, however, does not conclude anything regarding whether any interventions to reduce ABSI would reduce mortality risk independently, a question that would require randomized controlled trials to answer.