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1. Introduction
Adipose tissue is a well-known source of inflammation and a complex and highly active metabolic endocrine organ [1,2] that produces various hormones and metabolic factors [3,4,5]. Among various methods currently used to identify subjects at risk of excess adiposity are dual-energy X-ray absorption (DXA), isotopic measurement of body water, magnetic resonance imaging, whole body plethysmography, computed tomography, bioelectrical impedance analysis (BIA), and underwater weighing [6]. However, with the exception of BIA, these methods are costly, time-consuming, and often difficult to access. Other drawbacks to these approaches are their limited portability and repeatability.
A routinely-applicable indicator for the evaluation of body fat percentage (BF%), with higher sensitivity and specificity than classic anthropometric parameters (such as waist circumference (WC), body mass index (BMI), waist-to-height ratio (WHtR), and BF%), would be a valuable instrument for determining the presence of excess adiposity [7]. Such a technique would also be useful to validate methods and for clinical, epidemiological, and research purposes [8]. In this respect, in 2011 Bergman et al. [9] proposed a new method to determine BF%, termed the body adiposity index (BAI). The BAI-BF% is derived from hip circumference and height and was developed in a sample of Mexican Americans, following prior validation in a population of African-American adults [10,11,12]. Comparison with data obtained with a DXA device showed the BAI-BF% to be a valid predictor of BF%. Furthermore, Bergman et al. [9] also explored sex differences and, as expected, reported a higher mean BAI-BF% for females compared to males. The observed BAI sex differences correlated with DXA measurements. It has subsequently been widely used in clinical areas [13] and in research [14].
Substantial differences by sex in fat distribution are evident throughout the human lifespan [15,16]. While women predominantly accumulate subcutaneous fat, men amass significantly more visceral fat. Some of these differences are due to direct effects of sex steroids but also to the fact that there are numerous differences in the functionality of distribution of adipose tissue [17]. The relationships between sex-related phenotypes and different adiposity indexes have been studied previously [18], an issue that the original authors of BAI-BF% did not address. A recent cross-sectional study has reported a poor agreement between BAI- and BIA-based estimates of BF% in a sample of Colombian...