Here’s why BMI to measure health is wrong

When it comes to fitness and health, the world at large is obsessed with numbers. From tracking number of steps per day to tracking number of calories consumed, tracking heart rate to tracking number of reps in the gym, leading a fit lifestyle seems to be a game ruled by numbers.

Doctors, too, are obsessed with numbers, in fact the numbers that doctors stress about is at the core of all the other numbers that people chase on their way towards being fit and healthy.

The golden numbers that indicate whether a person is healthy, underweight, overweight or obese is the BMI (Body Mass Index).

Simply put, BMI is a measure of the proportion the body’s weight with respect to one’s height. This measure, though is currently being scrutinised. Several experts seem to questioning the accuracy of using this one single indicator to determine a person’s health and fitness status.

How did BMI become the indicator for healthy weight?

The BMI concept was developed way back in 1832 by a Belgian statistician Lambert Adolphe Quetelet, who was asked to come up with a description for an “average man” so that the government at the time could determine an estimate of obese people in the country’s general population.

Moving forward by another hundred years, this time to the United States, when life insurance companies started comparing weight in the average population among similar persons so they could calculate premium based on the “average” weight of the population and predicting a person’s hypothetical risk of dying.

This was a grossly unscientific approach and so psychologist Ancel Keys from United States, used the Quetelet measure to research nearly 7000 people and found that this measure was more accurate and far better predictor for healthy weight. It was also an inexpensive process.

Over time, Quetelet’s measure was renamed BMI and it came to be adopted as the primary indicator of healthy weight. It also helped when over time research indicated that those with increased BMI became more prone to several diseases of the heart, kidney, liver, diabetes, cancer and so on.

What is the BMI indicator?

Simple enough to do – divide your weight by the square of your height in metres.

The weight categories as per BMI scores are:

BMI of less than 18.5 – Underweight

BMI between 18.5 and 24.9 – Normal (Healthy)

BMI between 25 and 29 – Overweight

BMI over 30 – Obese

But is it still an accurate measure of health? The short answer to this is No. While it provides a broad overview to good health it cannot be the one-point single indicator to measure a person’s health. These are some reasons why:

BMI does not take into factor a person’s body-fat percentage. BMI only takes into account a person’s weight and cannot differentiate between muscle weight and fat weight. Muscle weight tends to be denser that fat. As a result, a person with muscle weight, training athletes can end up being misclassified as overweight, when in fact they are at the peak of their fitness. For example, as per BMI, Usain Bolt was almost overweight and if we went by only BMI scores, Tom Brady, American footballer would be termed obese.

BMI does not account for fat distribution. Sometimes a person can be in the normal BMI range but have fat stored in their stomachs, which can put them at risk for diabetes and heart diseases.

BMI does not take into account demographic or gender differences. All bodies are different, people from different countries have different body proportions. Even among men and woman the muscle vs. mass ratio is different.

So, what is the right way to measure health?

BMI is not a completely useless tool. It provides a broad overview of a person’s health and as such makes for a useful screening tool. But it is important that the factors listed above are also evaluated before deciding if a person is actually overweight or obese.

It would be effective to use BMI as the starting point and use other methods like calculating body fat percentage and analysing where the body fat is stored to provide a better solution to maintaining healthy body weight.



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