Two-dimensional predictive equation to classify visceral obesity in clinical practice

Nutrition Research Newsletter, Oct, 2006

The accumulation of adipose tissue, predominantly in the visceral cavity, plays a major role in the development of the metabolic syndrome, cardiovascular diseases, or both. Therefore, estimating visceral fat accumulation is important in terms of evaluating patients with a higher risk of cardiovascular diseases. One of the major priorities for obesity research is the improvement of identification of populations at risk from overweight and its associated complications, especially with a better characterization of the relationship between simple measures and metabolic alterations. Human obesity is heterogeneous with regard to topographical fat distribution. Analyses using computed tomography (CT) scan imaging indicate that human obesity should be classified into two categories: subcutaneous fat obesity and visceral fat obesity. Metabolic and circulatory disturbances are far more frequently associated with visceral fat obesity, which is at the same time more sensitive to caloric restriction and exercise therapy. However, visceral adipose tissue (VAT) assessment is not easy, and even though CT and magnetic resonance imaging are both reliable and accurate tools for determining body fat distribution, these techniques are expensive and often not suitable for clinical practice and epidemiological studies. Therefore, several studies have focused on the search for a simple, inexpensive, and reliable tool in central adiposity assessment that could be included as part of physical examinations in clinical practice when a quick measure is required and no economic resources are available or in epidemiological studies when population size is large. Such methods would include anthropometric indices such as BMI, waist circumference (WC), and waist-to-hip ratio (WHR), or other methods such as DXA and ultrasonography. There are no anthropometric tools that can measure VAT directly, and although a variety of anthropometric measurements have been developed to estimate central adipose tissue accumulation, no single parameter is generally considered as being accurate enough for assessing the metabolic risk associated with abdominal obesity. The purpose of this study was to develop a new two-dimensional anthropometric equation based on the elliptical model to classify visceral obesity in clinical practice and to compare the validity and reliability of the new equation with those of the circular model.

The researchers collected anthropometric and CT data from overweight/obese subjects (n = 61, BMI = 32.4 [ or -] 3.7 kg/ [m.sup.2]). A validation group of 32 subjects was also selected. An equation for the assessment of visceral obesity was developed using multiple regression analysis. Once validated, the equation was compared with previous models. Multiple regression analysis revealed that the sagittal and coronal diameters and the triceps skinfold were significant contributors to the model. The final equation was: visceral area (VA)/ subcutaneous area [(SA).sub.predicted] = 0.868 [ or -] 0.064 x sagittal diameter -0.036 x coronal diameter -0.022 x triceps skinfold. Patients with visceral-subcutaneous area ratio (VA/SA) > 0.42 were classified as having visceral obesity. The predictive equation was valid, showing a significant association with VA/SA assessed by CT (VA/SACT; r = 0.68;p < 0.0001). Paired Student's t test showed no significant differences with VA/SACT (p = 0.541). The reliability was high [F(24/60) =2.12;p=0.01].

Clinicians often wish to have data on different variables for which direct measurements without adverse effects may be difficult or even impossible. In this study, the multiple regression analysis performed to obtain an anthropometric equation to classify visceral obesity was based on the ratio between VA and SA suggested by Tarui et al. This index has been validated as a good index to assess metabolic alterations associated with visceral obesity. Data revealed that sagittal and coronal diameters together with the triceps skinfold were significant contributors to the model. Sagittal diameter has been widely proposed in the scientific literature as an accurate anthropometric measurement in the assessment of visceral fat. In this study, both coronal diameter and triceps skinfold were negatively associated with VA/SACT. Moreover, the Pearson's correlation test showed that they were positively associated with subcutaneous fat, whereas no significant associations were found with visceral fat.

The researchers conclude that the combination of sagittal and coronal diameters and the triceps skinfold give a reliable and accurate classification of visceral obesity. The application of the new predictive equation is valid to assess visceral obesity and is more precise and accurate than previous models such as the circular modEI, the elliptical model using different abdominal and back skinfolds, and even more accurate than the classical visceral obesity classification proposed by Tarui et al. The main technical advantage of the present anthropometric equation in clinical practice is that, unlike the other proposed models, it does not include subcutaneous abdominal adipose tissue thicknesses or waist girth, which has problems of location. From this study, the researchers classify visceral obese subjects as those individual with a [VA/SA.sub.predicted] > 0.42.

M. Garaulet, J. Hernandez-Morante, F. Tebar, et al. Two-dimensional Predictive Equation to Classify Visceral Obesity in Clinical Practice. Obes Res; 14;1181-1191 (July 2006) [Correspondence: Marta Garaulet, Department of Physiology, University of Murcia, 30100 Murcia, Spain. E-mail: garaulet@um.es]