Relative fat mass is a better predictor of dyslipidemia and metabolic syndrome than body mass index

In the past decades, the increasing prevalence of obesity is becoming a greater public health and health economic issue [1]. Obesity is a recognized risk factor for various cardiometabolic diseases and several indices are used clinically to assess the overall cardiometabolic risk [2]. BMI is traditionally the most widely used measure of obesity. Abnormal BMI is an independent predictor of mortality, and BMI is also used by some as part of the criteria for metabolic syndrome [3,4]. The main advantage of BMI is its simplicity to use both by clinicians and patients. It can also effectively rule out metabolic syndrome in certain populations [5]; however, the BMI is unable to differentiate between lean mass and fat mass, nor to consider body fat distribution. Other measures of adiposity consider body fat distribution, like waist circumference, waist-to-hip ratio (WHR) and waist-to-height ratio (WHtR), and more recently developed body adiposity index (BAI), none proved overall superiority [6–9]. In the light of the conflicting data, the best adiposity measure to help predict cardiovascular risk factors has remained controversial. Relative fat mass (RFM) had been recently developed as a new estimator of whole body fat percentages among American adult individuals of Mexican, European or African ethnicity. RFM is calculated using the equation: 64 − (20 × height/waist circumference) + (12 × sex); sex = 0 for men and 1 for women. Abnormal RFM (above 33.9 for women and 22.8 for men) showed promising results in its validation study. Compared with BMI, RFM better predicted abdominal obesity among men using dual energy x-ray absorptiometry as the gold standard; RFM was also found to be superior to BMI as a predictor of diabetes [10]. Only a few later studies were conducted using RFM as an obesity indicator. In a small trial, RFM was validated to estimate fat percentage among men and women with and without Down’s syndrome [11]. One study found RFM to be a better predictor of severe liver disease and mortality than BMI [12]. Our earlier reported results suggest RFM may be used instead of waist circumference to define metabolic syndrome [5]. Up to date, to the best of our knowledge, no further studies were published and the question whether RFM correlates better than BMI to metabolic disturbances is yet to be determined. The aim of this study, therefore, was to add to the body of evidence regarding the clinical applicability of RFM and to examine whether RFM is superior to BMI and correlates better with various cardiometabolic risk factors.