BMI, Body Mass Index.

How many of you have been to the doctor’s for a regular check-up and had your BMI calculated?

Or maybe you have gone on one of those scales at the gym or in boots which gives a little print out? They use BMI too.

I’m assuming most of you have, it’s fairly common practice.

Doctors and health practitioners love the BMI as it’s simple to understand.

Calculating someone’s BMI is one of the EASIEST ways of determining whether you are overweight, obese or underweight.

If you went to the doctors, and were told that your BMI was too high and you had to lose weight, many of you would do as we were told.

But before I go through a little story and the pros and cons of BMI I shall give you a bit of history about what it is and where it came from.

The History of BMI

The body mass index was designed by a Belgian man called Adolphe Quetelet over 150 years ago. BMI is defined as an individual’s body mass divided by the square of their height.

The formula looks like this:

BMI = Mass (kg) / (height (m))2

You can see here how to work it out by hand.

It was previously called the Quetelet Index, body mass index was the term used since the late 19th century. As it is such an easy thing to measure its popularity grew as an individual diagnosis tool.

BMI Figures


Very severely underweight - less than 15
Severely underweight - from 15.0 to 16.0
Underweight - from 16.0 to 18.5
Normal (healthy weight) - from 18.5 to 25
Overweight - from 25 to 30
Obese Class I (Moderately obese) - from 30 to 35
Obese Class II (Severely obese) - from 35 to 40
Obese Class III (Very severely obese) - over 40

Problems with BMI

I want to tell you a story about my friend Darren. I was in the gym a few weeks ago and I saw Darren, he had a really disappointed look on his face and asked if he could have a word.

He proceeded to tell me that he had had a health check done by the works doctor, and had been told he was obese and needed to lose three stone.

Darren weighs about 15 stone and trains regularly, I know him from when we played rugby, and he has always kept fit, whether it be sport, cycling or running, he always kept in good shape.

What did I say?

I told Darren that he was not obese and the doctor had made a big mistake and does not understand BMI. Let me explain…

Darren is muscular and an ex athlete, so BMI does not work for him and is not a good indicator of overall weight to height.

I knew BMI was problematic as I sit in the “over weight” category myself and I would class myself as quite skinny having around 8% body fat.

BMI was never designed to measure whether someone was overweight or underweight; it was designed simply to classify sedentary individuals with an average body composition.

So this tool (which is being used worldwide) was not even designed to serve this purpose.

One of the reasons that it is being used so much is because it is so simple, one of the reasons it’s useless is because it is so simple.

What do I mean by this?

I mean that that’s all BMI calculates is a person’s height and a person’s weight and that’s it. It fails to account for muscle mass, fat levels or any other useful determinants that suggest someone is at an unhealthy weight.

I could safely say that most professional rugby players would be graded as overweight or even obese according to their BMI. Would you say that these people need to lose weight? I don’t think so, it wouldn’t do their rugby any good!

It is far too general and it is way too easy to suggest someone needs to lose weight based on this one assessment.

Calculating it requires no fancy equipment, no time for health practitioners to calculate which is why it is so popular. This is another example of misleading ‘easy’ advice that we get in the healthcare system today. One size fits all.

BMI does not differentiate between a strong muscular athlete and a couch potato. BMI puts a professional boxer in the same category as a darts player.

There are so many different factors such as bone density, water weight, cartilage and muscle mass which affect a person’s weight that is not taken into account with BMI that it is no surprise it produces misleading results.

I would LIKE to think that if a clearly athletic person went to the doctors and was found to be categorised as overweight or obese according to their BMI the doctor would not tell them they need to lose weight, as happened in Darren’s case.

Something we do know is that the location where we store fat can be a big predictor of health risk. People who carry a lot of their excess weight around their stomachs and mid section (apple shaped) have been proven to be at high risk of suffering serious health problems. People who carry excess weight in their lower body (pear shaped) are less at risk.

BMI doesn’t take into account body shape. By identifying where the excess fat is stored can be very important in determining what changes the person will need to make.

Waist to hip ratio is a far better measure or just weigh and take a body fat reading, over 40% is obese.

A simple test to identify whether your body shape is the problem is by taking a waist circumference test. The average thresholds indicate that women with a waist circumference of above 88cm and men above 102cm are abdominally obese. We would get much more accurate measures if these two were calculated together.

It is not necessarily how much you weigh that causes problems, it is where the excess fat is stored that heavily influences the risk of health problems.

If you follow a healthy lifestyle you will train regularly and eat well, that is eat well and NOT starve yourself or even necessarily eat less, you can eat more if you know how. Also if you train the right way you will be mixing aerobic exercise with resistance training, this means you will be gaining muscle as you lose weight. This then means that the scales won’t be moving at a drastic pace, so there will be little difference to your BMI, BUT YOUR BODY SHAPE WILL CHANGE, even if the scales don’t at first.

Some people take up to 12 weeks before their body starts to lose weight, and I don’t know why, but after persevering, the flood gates open and things start to move eventually.

Most people don’t know the flaws with BMI and when told that it is high and they need to lose weight they will listen. Upon hearing that after all of their hard work their BMI hasn’t changed much it can be quite demoralising and ruin motivation despite the fact that they are much fitter and healthier and their waist line has decreased!

A study carried out at a Children’s Nutrition centre compared participants BMI results with results from a body fat percentage test. The study discovered that on average one out of four children labelled as obese according to their BMI actually had a normal percentage of body fat.

So next time you are in the doctor’s and they test your BMI and you are told you need to make certain lifestyle changes that you disagree with, then ask for some more tests.

It is important that all of us are treated as individuals and not thrown under an umbrella of a general calculation telling us if we are the right weight.

Thanks for reading and as always please share your views below the article.

Take care,


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