THE INDEX OF BODY FATS

[maria angelica sassone]

For decades, the Body Mass Index (BMI) is used as a simple tool that helps classify the suitability of a person's weight according to height. Faced with the ease of obtaining this information, the scientific community strives to introduce new tools to improve individual classification based on weight. In the quantification of the most reliable possible amount of fat a person and relate it to your individual situation based on age and sex. Besides the determination of fat content, other laboratory tests can be added to help define the degree of involvement on the overall health of an individual have that much fat. This will be able to identify situations that, in principle, be paradoxical after single application of BMI as adults with a healthy BMI (values between 18.5 and 25) are considered "thin, but obese from metabolic point of view. "

Autor: Por JUAN REVENGAFecha de publicación: 4 de enero de 2011Definition and measurement of obesity


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Obesity and overweight are defined as abnormal or excessive accumulation of fat that can be harmful to health, as holding the World Health Organization (WHO) . At the same time, for its extreme simplicity, most scientific societies, also the WHO itself, encourages the use of BMI as a primary tool for measuring obesity. However, their limitations are known in the scientific community and can make mistakes when considering classification as the only source of information.

The major limitation is that BMI does not consider the amount of adipose tissue, the variable that defines the overweight or obese
His main problem is not to consider directly the amount of adipose tissue, ie the variable that defines being overweight or obese. Generally, an excess of adipose tissue causes an increase in weight (BMI variable used), but not all people with high BMI are overweight or obese. Conversely, you can also arise where he retains a healthy BMI understood, however, a high proportion of fat to the recommended amount for your circumstances. In the latter case belong those who, although considered thin, suffering the metabolic consequences of excess fat similar to the group of patients considered obese.

But this is not the only limitation of the IMC. The classification known values of this index for adults serve a population with a very wide age range of 20 to 65 years, without any differentiation in this broad age group. Similarly, these values are used regardless of the sex of the patient. This is a significant bias or limitation of this tool, which has been shown in multiple studies and is reported in a recent article published on the website "PLoSOne", the so-called Public Library of Science (Public Library of Science).

The index of body fat now
Body Fat Index (IMF) allows a more accurate to label the different people depending on the degree of obesity. To obtain, similar to BMI, divide the total weight of body fat a person from their height squared. Unlike BMI, the scale of values of the IMF differs between the sexes and is suitable for narrow age ranges.

The scale of values of the IMF differs between sexes and fits narrow age ranges
The good prospects in using this new value are shown in the United States from the National Survey of Health and Nutrition Examination 2008 (NHANES), which in a separate investigation of the survey compared the classification obtained with BMI and the IMF in more than 5,000 people. After the comparison, were in evidence some of the "errors" BMI classification.

Similarly, in an article published last October in the American Journal of Human Biology, "the IMF measured in 538 subjects defined with greater precision the situation of overweight or obese, compared to the results obtained through IMC.

However, most studies attempting to highlight the shortcomings of the BMI and the virtues of the IMF calls for caution in their use. So far there is no standardized categorization, so universal, the IMF established criteria, such as in the case of the IMC. At the same time, many of these studies have certain limitations regarding the sample participating in the study (age, ethnic or very specific). Therefore, it is suggested that in future more research should be conducted in different populations, in order to make the IMF a global tool to precisely defined criteria.

Getting the value of fat mass
Undoubtedly, most of the limitations of the IMF lies in the difficulty of estimating the fat content of a person for the proposed index. While calculating BMI is simple (just have a scale and a stadiometer), get the fat a person is not exactly easy. Currently, some methods have become popular that long ago were not as accessible. One method that enjoy relative accessibility is bioimpedance , which with a similar format to a scale, gives a figure of the percentage that represents the total fat weight. In this method, there is a significant difference between the devices that are sold for home use with respect to implementing them in health, much more reliable, accurate and generally higher price.

The major limitation of the IMF lies in the difficulty of determining the fat content of a person
Other tools used exclusively for professional applications are absorptiometry, dual X-ray absorptiometry (DEXA or DXA), the bod-pod or plethysmography , the computed tomography (CT) and magnetic resonance imaging. Among them, besides the bioimpedance, DEXA and bod-pod are used more often to the determination of fat mass in the clinical setting, a value that, subsequently, to find the index of body fat.

THIN, BUT FROM OBESE THE METABOLIC VIEWPOINT
The detection of a population group that maintains a normal weight, healthy appearance, but because of its higher fat content shares a large part of complications related to obesity, part of a 1981 article published in the American Journal of Clinical Nutrition. " Since then, numerous investigations have been conducted in this particular population.

In 2007, a review of this subject published in the journal Applied Physiology, Nutrition and Metabolism "concluded that these patients had a greater amount of abdominal fat and visceral than the control subjects, which leads them to an increased risk for Type 2 diabetes and cardiovascular disease .