BMI Correlates Better to Visceral Fat and Insulin Sensitivity Than BAI

Abstract

TO THE EDITOR: BMI has been used for a long time but is often regarded as an inadequate measurement of obesity. Bergman et al. in their article “A Better Index Of Body Adiposity” (1) developed the body adiposity index (BAI) from hip circumference and height only to reflect the percent body fat, as measured by the dualenergy X-ray absorptiometry. Although BAI is highly correlated with percent body fat, the relationship of BAI and visceral adipose tissue is currently unknown. We investigate the relationship of BAI and visceral adipose tissue and compare with the performance of BMI. The participants were mainly healthy volunteers in Taiwan Life Study cohort (2). Abdominal adiposity was measure by noncontrast computed tomography. Subcutaneous abdominal fat area and visceral fat areas were measured on one cross-sectional scan obtained at the level of umbilicus (3). Total abdominal fat area was defined as the sum of subcutaneous and visceral fat area. BAI was calculated as (hip (in cm)/(height (in m))) − 18 (1). Pearson’s correlation coefficients were calculated among BAI or BMI and total abdominal fat area, subcutaneous abdominal fat area, and visceral fat area. Body fat area was logarithmically transformed for statistical analysis. A bootstrap resampling method with 1,000 replications was used to compare the correlation coefficients. Insulin resistance was calculated by fasting insulin and sugar according to HOMA2 method as proposed by Levy et al. (4). The statistical analyses were performed with Stata/SE 11.0 for Windows (StataCorp LP, College Station, TX). There were 424 participants, including 151 men and 273 women. The mean (s.d.) age, BMI, BAI, total abdominal fat area, subcutaneous abdominal fat area, and visceral fat area were 52 (12), 24.1 (3.3), 29.2 (4.2), 279 (11) cm, 179 (72) cm2, and 100 (55) cm2, respectively. As shown in the table, BMI and BAI correlated significantly to body fat. However, BMI correlates better to total abdominal fat area, visceral fat area, visceralto-subcutaneous abdominal fat area ratio, and HOMA2-IR than BAI in both genders. The relationships of subcutaneous fat area to BMI or BAI were similar in all subjects but showed better correlation with BMI when compared separately in men and women. In present study, we found that BMI correlates better to visceral fat than BAI. Visceral fat area, as measured in a singleslice computed tomography scan, has a closer relationship than subcutaneous abdominal fat area or total fat area to the development of adverse metabolic and cardiovascular events (5,6). Indeed, BMI also correlates better to insulin sensitivity index HOMA2-IR than BAI in our population. Therefore, based on the findings from Bergman et al. and ours, further study is needed to clarify the relationship between BAI and adverse metabolic and cardiovascular events.