**2. Obesity: how it is classified**

As the direct quantitative and/or qualitative analysis of the body fat contents (i.e. white adipose tissue type, WAT) is associated with some erroneous interpretations, and "body mass index" (BMI), which serves as a simple weight-to-height ratio (measured as kg/m<sup>2</sup> ), is nevertheless typically used to classify overweight and obese adolescents and adults. Consistent with this concept, the World Health Organization (WHO) has published international standards, by which one may classify, with a certain degree of precision, overweight and obesity in adults. The condition of obesity is measured as a BMI value larger than 30 kg/m<sup>2</sup> ; however, it can be further subdivided according to the severity or the "degree" of excessive weight [1].

Even though the BMI value furnishes health professionals with a straightforward and simple estimation of obesity, a far more useful "interpretational" aspect of overweight resides with the regional localization of excessive, white type of body fat (WAT). Both the mortality rate and morbidity incidence vary substantially with the distribution of bodily fat, yielding the highest possible health risk associated with enlarged abdominal fat depots (i.e. so-called central obesity). This type of obesity, which is related to WAT contents, is associated with a plethora of diseases/ailments, encompassing debilitating conditions like cardiovascular disease (CVD), as well as non-insulin-dependent diabetes mellitus (NIDDM). The impact of central obesity, accompanied with a lower amount of brown adipose tissue (BAT, which normally burns and

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© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, rarely stores fat as triglycerides), clears in populations (e.g. Asian) who display a tendency towards relatively low BMI values but rather high levels of abdominal fat, which make them particularly prone to NIDDM, high blood pressure (hypertension) and coronary heart disease (CHD). Studies of various Asian populations recently revealed that some 20% of adults, not already classified as being overweight or obese, still displayed marked central obesity, rendering them more prone to develop or incurring these associated disease states. Other methods of analysis measuring abdominal fat are available, such as ultrasound recordings, waist circumference and/or waist-to-hip ratios (WHR). However, unlike BMI values, these are rarely measures routinely, but alterations observed with waist circumference do reflect altered risks for developing CVD, as well as other chronic diseases. As with BMI, cut-off values have been shown to identify enhanced risks; however, for waist circumference observations, these are both sex and population specific. Hence, as the risk prediction varies from one population to another, single global values cannot easily be applied with high precision [2].
