By Seema Gupta, MD, MSPH
Primary Care Physician,
Charleston, WV
Dr. Gupta reports no financial relationships relevant to this field of study
SYNOPSIS: A large international study found frequent discordance between body mass index (BMI) and waist circumference (WC), driven by the substantial variability in visceral adiposity. Within each BMI category, patients with the highest WC were more likely to have higher cardiometabolic risk.
SOURCE: Nazare JA, et al. Usefulness of measuring both body mass index and waist circumference for the estimation of visceral adiposity and related cardiometabolic risk profile (from the INSPIRE ME IAA Study). Am J Cardiol 2015;115:307-315.
Worldwide, the prevalence of obesity has reached epidemic proportions. This epidemic is not simply a consequence of poor diet or sedentary lifestyles, but is a complex, multifaceted state in which environmental, biological, and genetic factors all play essential roles. Increased body mass index (BMI) is associated with higher all-cause mortality compared with normal weight individuals, as well as mortality from cardiovascular disease. Abdominal adiposity is recognized to be associated with a number of conditions leading to increased cardiometabolic risk (CMR). Studies have demonstrated that measuring the indices of abdominal adiposity, such as waist-to-hip ratio (WHR) and waist circumference (WC), may be superior to BMI in detecting CMR in both sexes.1 Measuring WC is a simple procedure requiring a tape measure. However, researchers do not completely agree and have questioned the clinical relevance of measuring WC instead of BMI to assess cardiovascular disease risk, since both BMI and WC have been found to be highly correlated and each can independently predict CMR.2 When conducting assessments of central adiposity, directly assessing visceral adiposity tissue (VAT) by computed tomography allows more accurate evaluation since VAT is more metabolically active than other adipose tissue sites and appears to contribute to many metabolic abnormalities associated with weight gain.
In their study, Nazare et al evaluated the relevance of adding WC to BMI for the estimation of VAT and CMR. Between 2006 and 2008, 297 physicians recruited 4504 patients from 29 countries. Final analysis included data from 4109 patients. Researchers measured both BMI and WC and assessed VAT and liver fat by computed tomography.
The study found that although there was a strong correlation between WC and BMI, about 30% of participants displayed discordant values for WC and BMI quintiles (r = 0.87 and r = 0.84 for men and women, respectively, P < 0.001). VAT and WC showed considerable between-subject variability within each BMI category. Increasing gender-specific WC tertiles correlated with significantly higher VAT, liver fat, and a more adverse CMR profile within each BMI category.
Within each such BMI category, patients with the highest WC were more likely to have higher liver fat content, high-sensitivity C-reactive protein, and prevalence of type 2 diabetes mellitus, in addition to the classical risk factors. Authors contend that this finding in the study may provide further support for the hypothesis that the increased cardiovascular risk may be due, in part, to the excess VAT and liver fat, contributing to atherosclerosis, insulin resistance, and inflammation. They also hypothesize that based on findings, patients with high WC and low BMI may be more prone to VAT accumulation and CMR abnormalities, irrespective of ethnicity.
COMMENTARY
In recent years, there has been an increasing debate over which measure of overweight and obesity is best able to discriminate those individuals who are at increased CMR and visceral adiposity. While BMI is currently widely utilized as an index of general adiposity, measures of central adiposity, such as WC and WHR, may be superior in assessing these risks.3 The current study conducted across several nations and ethnicities demonstrates that for any given BMI value, both men and women display substantial inter-individual variation in WC, revealing important differences in VAT and liver fat. This may explain the discordance between WC and BMI values observed.
While it has been debated whether WC should be measured in addition to or instead of BMI, the study clearly makes a case for measuring both since these two parameters seem to provide separate but important information.
This may be an example in which a strong correlation between BMI and WC at the population level may not necessarily imply the same at the individual patient level. The combined use of both measures in an office setting would allow for clinical stratification of patients based on their CMR, VAT, and liver fat content at a given BMI. This approach may be better able to provide an assessment of visceral adiposity and CMR of the individual patient.
REFERENCES
-
Ashwell M, et al. Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: Systematic review and meta-analysis. Obes Rev 2012;13:275-286.
-
Balkau B, et al. International Day for the Evaluation of Abdominal Obesity (IDEA): A study of waist circumference, cardiovascular disease, and diabetes mellitus in 168,000 primary care patients in 63 countries.
Circulation 2007;116:1942-1951.
-
Browning LM1, et al. A systematic review of waist-to-height ratio as a screening tool for the prediction of cardiovascular disease and diabetes: 05 could be a suitable global boundary value. Nutr Res Rev 2010;23:247-269.
