Sunday, September 16, 2012


Body Mass Index, better known as BMI world over, is supposed to be a marker for considering whether a person is healthy, over weight or obese and this has stood the test of time for decades without seriously being challenged by any other more appropriate body health monitor. BMI was first suggested by Adolph Quetelet, the reputed Belgian mathematician of nineteenth century, around the year 1832, for comparing the health conditions of people based on the body parameters, height and weight and it was known as Quetelet Index or QI. As it became the golden standard since then, the only change that was seen subsequently was changing the name to Body Mass Index in 1972 to make it more explicit and reflect its relation to human health. There are some variants of this evolved later like Fat Free Mass Index (FFMI) and Fat Mass Index (FMI) which take into consideration the influence of body fat in distorting the BMI values. In spite of all these developments BMI is still the universally adopted testing protocol for body weight related problems in populations around the world.

BMI is the ratio of the body weight to the square of height of a person and both Metric and British measuring units can be used to arrive at the figure. For example a person with a weight of 75 kg and height of 1.7 meter is deemed to have a BMI equal to 75 divided by square of 1.7 which comes to 28.9. If British units are used it must be weight in pounds divided by square of height in inches. According to present norms a BMI figure between 18.5 and 25 is considered optimal and if the same is outside this range remedial steps are called for to correct it through appropriate measures. While BMI less than 18.5 is considered to represent underweight, any value above 25 is not taken as normal. In to days world when the number of obese people is increasing at a phenomenal pace through out the world, especially among populations in affluent countries, values of BMI are very relevant to assess the healthiness of people. BMI values 25-30 represent over weight, 30-35 moderately obese (Class I), 35-40 severely obese (Class II) and beyond 40 very seriously obese or morbidly obese (Class III). Obese people do need medical attention while morbidly obese people may even require surgical intervention like gastric banding. According to social scientists monitoring the heavy damage caused by obesity in a country like America, same may work out to $ 344 billion by way of increased medical bills and $ 73 billion through lost productivity!

BMI Prime is another mathematical tool to compare body weights among the population though it is not clear why there should be another such yardstick when BMI monitoring has served the world admirably well for the last 180 years. BMI Prime is the ratio between the actual calculated BMI value and the optimal BMI value of 25 and when it is 1 body weight is considered normal.  Aberrations in BMI values do occur in many cases and there is some ambiguity as to how far they are true reflection of health status at least in some people. For example athletes with high lean body mass invariably show higher BMI figures while they are actually very healthy. Same is true with people with varying body frames but same weight. When it comes to Asians, in stead of BMI of 25 as normal, the recommended optimum BMI value is 23. Fat levels in the  body, especially the visceral fat is not considered in the BMI calculations as it very significantly plays a role in obesity and there fore the protocols like FFMI and FMI are being mentioned as more appropriate to determine the body health of the population. 

As fat levels have great influence in body weight changes, many health experts believe BMI needs to be linked to the body fat content some way to reflect the real health of a person. Total body fat varies any where from 20% to 30% for human beings with women having almost one and a half time that of men. If the body fat content exceeds 32% it is considered as reflecting  real obesity in women while in case of men values above 25 indicate on set of obesity. But measuring body fat is not that easy because of enormous variations encountered with different techniques available to day. Hydrostatic weighing or underwater weighing is often considered as most reliable method of fat assessment in human body though other techniques like skin fold measurement, body girth determination, body impedance, air displacement method, body scanning etc are also deployed for the same purpose by different investigators.   

All said and done, there are still gaps in the science of assessing obesity though BMI, the mainstay of medical research on body size and its relationship to health. But while the BMI is a fine measure of a large population's tendency toward illness and early death, it's a poor predictor of those outcomes in individual patients. According to a new study waist circumference may be a better predictor of health as it is an indication of presence dangerous fat deposits around visceral organs though measurement of this parameter is not easy as discussed above. The new paradigm called A Body Shape Index with the acronym ABSI is calculated as waist circumference in centimeters divided by the product of multiplying the square root of height in centimeters with cube root of BMI. If those who developed ABSI are to be taken seriously, this new technique can predict the chances of those who face higher risk of death within the next five years as per their extensive field studies of thousands of people with varying degree of over weight. It is known that those who are obese are more vulnerable to diseases like Type II diabetes, CVD and some types of cancers but the danger is more from the the unwanted fat deposits which are now factored into ABSI. With over 78 million adults and 12.5 million children reported as obese in the US, this country has a vital stake in developing this tool further to save enormously in terms of saved lives and wasted resources. 


1 comment:

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