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The facts about BMI

Body Mass Index or BMI is an equation designed in the 19th Century by a mathematician and statistician named Adolphe Quetelet. It's original use was as a fat guide for large population groups for demographic planning needs. This was quickly adopted as an individual patient’s obesity measurement method by the medical professions and remained unquestioned until the 1970’s where better technology and more accurate resources cast doubt on its usefulness.

It remains the most used weight guide in Doctor’s surgeries and hospitals because it is a quick and handy chart but this weight scale has come under increasing scrutiny over the last 40 years. In essence, it's an exact figure found by dividing your weight in Kg by your height in m².

You’ll find it taken most often by medical professionals. It’s a useful measurement to be aware of because in some cases medical and surgical procedures may be denied to people whose BMI is not within a desired safe zone. Many health and fitness professionals believe that BMI is inaccurate and impractical for several reasons:

  1. The equation used becomes less accurate the taller or shorter you are. This means that a shorter person will believe themselves to be of a lower BMI and the taller person to be a higher reading.

  2. BMI does not account for body type. A broad shouldered man of average height will most likely have a greater BMI score than a smaller framed woman of the same height. This risk is further increased in someone who gains muscle easily.

  3. Neither does BMI consider muscle mass. A well conditioned sportsperson who trains for power based sports such as sprinting or rugby will carry more muscle and have an overweight BMI reading despite being at the peak of their physical fitness.

  4. A BMI score is an exact number and can be used as a cut off point at which some medical decisions are made. For example, a BMI of 30 may be required for IVF treatment. This would not account for the lifestyle changes a person may make to achieve this figure. Is a person who has lost 5 stone through careful diet and exercise less worthy of IVF treatment than a person whose poor eating habit has kept her slimmer?

So why continue to rely on such an outdated and potentially inaccurate system?

It’s cheap, it’s quick and for a large part of the general population it’s accurate enough for basic health assumptions to be made.

Also, it is rarely taken as a measure of health on its own. A health or fitness professional who is measuring your BMI is likely to be also asking you other health related questions and noting your general physical condition.

BMI charts are strong visual tools to demonstrate a person’s health as they tend to show sweeping arcs of green, amber and red. It is easy to make a large statement in a short time by showing someone their place on the BMI chart and this gives strong motivation to reach the desired green arc of healthy body weight.

While it’s important to be aware of the limitations of the BMI reading, it continues to be a fast and effective gauge of obesity for the greater majority of the population and will most likely give you a good starting point for weight management. Regardless of what you hear about BMI, don't rule it out just yet. It's a handy guide for anyone looking to lose weight.

Enjoy Good Health!

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