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Can you rely on the BMI?

Published : Thursday April 12, 2012 | Posted in : General Health
Highlighted BMI text

The body mass index is a contentious calculation in modern healthcare. Designed as a straightforward tool to simplify weight categorisation, the BMI scale continues to divide opinion in regards to its accuracy and importance when it comes to determining whether someone is overweight or obese. The debate that sounds the BMI scale centres on how accurate it actually is in real terms.

Health professionals use the body mass index precisely because it is so simple, allowing them a quick method of calculating whether an individual is of a healthy weight. The only information that is required is the height and weight of the patient. Depending on where a person falls on the BMI scale, they will be classed as either severely underweight, underweight, normal weight, overweight and obese. The accuracy of these classifications is called into question because there is no way for it to factor in body fat percentages, meaning that some groups of people, such as athletes with a high muscle mass, are erroneously classed as overweight. The BMI scale also fails to take into account other important factors that can affect whether a person's weight is "healthy" or not, such as age, ethnicity and gender.

The debate is by no means new, but it was reignited last week when a report raised more concerns about its usefulness. The research also warned that current estimates about obesity levels could actually be too low, as the BMI scale was classifying people as overweight when they should actually be classed as obese. The researchers, at the Weill Cornell Medical School, compared the calculated BMI scores of almost 1,400 adults who were patients at a private health clinic in New York with the results of a measurement that combined body fat, bone density and muscle mass. The latter calculation requires a blood test and something called a Dual Energy X-Ray Absorptiometry (DXA) Scan. According to the researchers, this comparison revealed that the BMI scale was incorrect in its classification of 50% of women and 25% of men.

bmi graph

So does this mean the BMI scale should be scrapped? In my opinion, no. Though this study may raise some fair points relating to how accurate the BMI scale is, the alternative it offers does not offer the same combination of simplicity and accuracy that the BMI scale presents. The key benefit of the BMI scale is the fact that anyone can calculate it on their own, without even needing to visit a doctor. It is true that this may mean the result is not always completely accurate, but it is worth considering that it is only meant to be used as an indication of obesity. If a BMI score indicated that an individual was obese, other tests would likely be administered by that individual's doctor to confirm this, and also to check for other important health conditions associated with obesity such as high cholesterol.

To put this simply, the BMI is a helpful tool to assist in diagnosis, not a diagnosis in itself. The problems only arise when its results are given too much weight.

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