Index of central obesity – A novel parameter
Introduction
Central adiposity has shown a strong association with type 2 DM [1], IR [2], components of metabolic syndrome (MS) [3], [4] and ischaemic stroke [5]. Waist circumference (WC), has also been shown to strongly correlate with hypertension, type 2 DM [6] and all the criteria for MS [3]. WC has been used as a parameter of central obesity in various risk scores and definitions of MS. Following the concern that NCEP ATP III criteria, applied to the Asians, will underestimate the population at risk [7], modifications in WC cutoffs as 90 cm in men and 80 cm in women were suggested [8]. Recently International Diabetes Federation (IDF) has defined metabolic syndrome in which race specific cutoffs for WC are suggested separately for males and females [9]. Though this need for lower limits of WC in Asians is attributed to ethnic differences, it was observed that even within the same population, people with identical WC but different heights have dissimilar risk for hyperglycemia, hypertension and fatty liver [10]. Moreover risk of MI was found to be greater in short than tall men [11] and women [12]. The ethnic difference that has led us to lower cutoffs may be essentially attributed to differences in average height. For a given WC a short person will obviously look more centrally obese than a taller person. Though WC can roughly quantify amount of truncal fat, it cannot effectively gauge its contribution to whole body fat. For the same reason WC is not applicable to quantify central obesity in children.
Section snippets
Hypothesis
Therefore we propose that, to quantify central adiposity (central distribution of fat), height, as a parameter must be taken into consideration. Here we hypothesize that index of central obesity (ICO) defined by us, as a ratio of WC and height correlates better with central obesity than WC alone. It is important to include height as a denominator, as other areas in body have effects opposite to that of fat in central region. WC alone can quantify fat in central region, but would miss the
Evaluation of hypothesis
Using average heights of various countries and WC cutoffs suggested by IDF for the country, ICO was obtained separately for males and females (Table 2). The ICO cutoffs obtained ranged from 0.51 to 0.58 among males and 0.47 to 0.54 among females. This novel parameter narrowed down the wide range of WC cutoffs suggested by IDF, which vary from 90 cm to 102 cm for males and 80 cm to 88 cm for females. The small difference in cutoffs obtained for males and females may even allow us to have a common
Pilot study
In a pilot study we compared body fat distribution in two persons of identical WC and BMI but of different heights. We present its correlation with ICO, in this pilot study to test the putative concept.
Study design and methods
Two subjects, Dr. P (First Author) and Mr. X, were selected. Both have identical WC and BMI, but different heights. Clinically all major medical disorders were ruled out. Neither was on any drug that would potentially alter body fat composition. Complete physical examination was performed and auxological parameters like height, weight, BMI and WC were measured. WC was measured in full expiration at the level of the narrowest part between lower border of rib cage and iliac crest. Photographs of
Results
On visual impression the subjects clearly appeared to differ in their body fat distribution. Dr. P looked generally obese and Mr. X was obviously centrally obese (Photograph 1). WC (98 cm) and BMI (28.8) were identical for the two. Total body fat of Dr. P was 26.2 kg while that of Mr. X 15.8 kg (Table 1). Their truncal fat was 9.5 kg and 7.4 kg, respectively, though percentage of total body fat contributed by truncal fat was 36.11% and 46.31%, respectively. On investigation Dr P had normal glucose
Discussion
Off late significant emphasis has been laid on central adiposity and many studies have shown a strong correlation of WC with all derangements related to IR. WC is the only auxological parameter, included in NCEP diagnostic criteria for MS. In view of suggestions that gluteofemoral fat [13], leg fat [14] and muscle mass are protective against IR, contribution of central fat in the total body composition becomes all the more important. For quantifying it, height must be considered in addition to
Conclusions
ICO can supplant WC as a better parameter of central adiposity and perhaps even eliminate the confusion emanating from lack of consensus on race-appropriate cutoffs. Even at individual level, ICO probably can quantify central obesity more accurately, height being considered as a variable. It may even do well if used in different risk scores like diabetes risk score, in place of WC. It may be effective for quantifying childhood central adiposity as well.
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