BMI – What is it? Explained

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What does ‘BMI’ stand for? What do the various BMI categories mean?

BMI stands for Body Mass Index. It gives you an idea of how your weight compares to common values and is calculated as your weight (in kilograms) divided by the square of your height (in metres) or BMI = kg/m2

Normal weight ranges: Body mass index (BMI):

    Underweight : BMI is less than 18.5.

    Normal weight : BMI is 18.5 to 24.9.

    Overweight : BMI is 25 to 29.9.

    Obese : BMI is 30 or more.

What does a BMI tell doctors? Are there limitations in what it tells us?

BMI is a useful tool that allows doctors to objectively look at weight and evaluate how this affects risk of diseases that are linked to obesity or being underweight. Together with other tests, BMI values can be helpful when discussing healthy lifestyle measures and treatment options.

There are limitations when using BMI that need to be considered. The measurement is based on an average distribution of body fat, including ‘intra-abdominal fat’ – the fat deep inside your stomach cavity rather than under your skin. This intra-abdominal fat has been linked to type 2 diabetes and heart disease. People of Asian origin, have higher intra-abdominal fat, so BMI calculations will give inaccurately lower readings. For this reason the World Health Organisation has recommended that some Asian groups should be considered overweight if their BMI is 22-25, and obese with a BMI of 26-31.

Likewise for people who are very muscular BMI may be inaccurate as these people have lower body fat levels, which means BMI results may be inaccurately high. For people over 60, muscle mass tends to drop and body fat rises so this will affect BMI calculation and should be taken into consideration.

Alternatives to BMI are ‘waist to hip’ and ‘waist to height’ ratio, which take into account intra-abdominal fat and abdominal waist circumference. A recent study found that the most accurate way of predicting your whole-body fat level was waist to height ratio.

Can we calculate BMI for children?

Yes – BMI can used for children using the same calculation, however it is interpreted differently compared to adults. Age and gender specific percentile charts are used to interpret a child’s BMI and show a child’s relative position among children of the same age and gender. BMI calculations in children are mainly used if there is a concern that a child may be under- or overweight.

What are the risks associated with a high BMI?

Having a high BMI and being in the ‘overweight’ or ‘obese’ category, significantly increases your risk of a number of medical conditions including type 2 diabetes, heart disease and cancer.

What are the global trends of BMI in western countries?

It is evident to see that the global trend of BMI in Western countries is rising mainly due to the over consumption of food. Consequently there has been a rise in medical conditions related to obesity. In the United States obesity is responsible for 6%–10% of national health expenditures and is 2%–4% in other developed countries.

Can I calculate BMI myself?

Yes you can. This is very simple to do and there are many online tools that can be used for free. All you will need is your height (m) and weight (kg). Plug these into the calculator and away you go.

Christmas is coming…what should I do in the New Year to reduce my BMI?

Rather than waiting for the New Year and vowing to get back to the gym in January, make realistic and sustainable changes now. Walk the few stops instead of taking the bus to your destination, use the escalator instead of the stairs or set a timer and get up from your desk every so often to walk around the office than be sitting at your desk for hours on end. To take it further, find a sport you enjoy that does not feel like a chore and that fits into your lifestyle. If you enjoy it then hopefully it won’t be yet another New Year’s resolution that is unsustainable!