Thursday, May 2, 2013


Body Mass Index or more commonly known by its acronym BMI is considered a sacred cow which no one wants to question. It is supposed to make a value judgment regarding the status of health one enjoys and what dietary modifications are called for in rectifying any abnormalities reflected by the BMI value. Though it was evolved 150 years ago, many suggestions made from time to time were not acceptable to a vast majority of health pundits and medical community. One of the uncertainties about the reliability of BMI is that it does not differentiate between weight caused by fat and muscle with the possibility some normal persons may be bracketed as over weight while some unhealthy persons may be categorized as normal. Also questionable is the arbitrary figures adopted in different countries for classifying people a over weight and obese. Latest suggestion to modify calculation of BMI uses a different equation to factor the height more realistically into the calculation. How far the new formula will yield better and more accurate result remains to be seen. Here is a take on this new development.      

"Any system that tells people whether they are "normal", "underweight", "overweight" or "obese" is bound to be controversial, but one obvious weakness of the BMI is that it doesn't distinguish between fat and muscle.First devised by Adolphe Quetelet more than 150 years ago, BMI is calculated by taking your weight (in kilograms) and dividing it by your height squared (in metres). The body-mass index that you (and the National Health Service) count on to assess obesity is a bizarre measure... As a consequence of this ill-founded definition, millions of short people think they are thinner than they are, and millions of tall people think they are fatter.
    * Prof Trefethen's letter in full (third in list)
    * His explanation of his formula
But mathematician Nick Trefethen, Professor of Numerical Analysis at Oxford University, thinks that the old formula is wrong, as he explained in a letter to the Economist newspaper published earlier this month. He thinks that people have put too much trust in it in part because it looks so precise - like, say, Einstein's famous equation E=MC². "That's an equation of physics and it's really right. The BMI formula looks similar. It seems to have the same character but it doesn't reflect a precise truth about our world, it's an approximation to a very complicated reality," he told the BBC.
With that in mind he has proposed a new formula: 1.3 x weight, divided by height to the power 2.5".

No matter which equation is used human body is so diverse that it will be difficult to classify them based on any single formula. The extent of muscle and fat present in the body is difficult to be assessed and therefore BMI can at best be an approximation of the state of health of a person at any given time. In the case of fat too, quality and the location of this component will decide whether weight contributed by fat is good or bad. Under such an uncertain situation BMI is still a good reckoner or indicator regarding the health status of most people. Those with high BMI can always go for further diagnostic tests to decide whether they are healthy or not.    


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