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jks marven
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8:57 AM on June 10, 2008
deepa iyer's Answer
There is a clear link between body weight, or more specifically high body mass index (BMI; kg/m2) and the risk of morbidity and mortality1. A high BMI is associated with several abnormalities now ollectively referred to as the metabolic syndrome2, in which insulin resistance with excessive adiposity appears to be the central pathogenic factor. Adiposity is usually inferred from the BMI; however, this may not be sufficient to fully explore relations between body fat and alterations in human health. It would appear that the body composition, rather than body weight, determines the risk for diseases associated with ageing and other chronic diseases1, as well as mortality3. The BMI cut-off point that identifies the proportion of people with a high risk of non-communicable diseases (NCD) is a desirable indicator, because it will provide policy makers with information to initiate prevention programs, and assess the effect of public health or clinical interventions4.
BMI – DISEASE RELATIONSHIP AND ITS IMPLICATIONS
The inappropriate accumulation of body fat is intrinsic to the development of chronic disease when body weight increases. The definition of overweight and obesity uses BMI (25 kg/m2 and 30 kg/m2 for overweight and obesity respectively) as the criterion1. This has been adopted globally by public health, researchers, dieticians and clinicians. There are several questions that need to be answered in this context, however. For instance, is there a continuum of increasing risk with increasing BMI, or is there a BMI cut off that determines the risk? The analysis of most BMI–disease relationship curves will show that it is difficult to decide on a single inflection in the relationship, that defines a cut-off; so the World Health Organisation (WHO) Expert Consultation on BMI acknowledged that a continuum exists4. The next question is: For what outcome should the BMI cut-off be used? For example, it is not entirely clear whether BMI is a reliable predictor of a mortality outcome5. Other than mortality, which is a unique and easily documented outcome, does the BMI cut-off apply to all other disease outcomes? A recent study of sick leave in a Belgian workforce suggested that BMI was not a determinant of days taken off sick, while waist circumference was6 (Tables 1, 2). The question then is, does the BMI paradigm refer to excess adiposity alone or to the location of the fat as well? This was a concern for the WHO Expert Consultation, which suggested that action points based on BMI should be refined, where possible, with measures of central adiposity4. A detailed discussion of the issue of fat location is beyond the scope of this paper, but briefly, waist circumference has shown to be a reliable indicator of absenteeism due to sickness6. While some have shown the waist – hip ratio to be a better predictor of cardiovascular mortality7 (Figure1), others have shown that the waist and hip have independent and opposite effects on risk for cardiovascular disease8. Finally, if adiposity is the sine qua non of the BMI disease relationship, is it better to have body fat cut-offs? The body fat percentage varies with different races and ethnicities, as well as with age and circumstance (Table 3); risk evaluations have attempted to define cutoffs for the body fat in relation to the metabolic syndrome9.
When these issues are viewed through a prism of differing genotypes, phenotypes and hazard exposures in Indian communities (Figure 2), the fundamental question still arises: “Is it important to have specific Indian BMI cut-offs?” In order to answer this question, we need to explore the body composition (specifically body fat) to BMI relationship in Indians.
Answered at
7:32 PM on June 12, 2008
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