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What Does Your BMI Really Mean?

By Edited Dec 25, 2015 1 2

If you are on a journey to lose weight, like me, you will be interested in your BMI. One of my goals is to hit the healthy BMI – that is when I will start finalising my weight loss goals. But, what does your BMI really mean? Is it something that you really have to listen to?

The truth is, a few years ago I wasn’t interested in this. BMI – or Body Mass Index – is not an accurate way to tell if you are healthy or not. It simply measures your weight in relation to your height. Those who are shorter should have a lower weight than those who are taller. However, there are many problems and inconsistencies with it.

slim waistline
Credit: Ambro/Freedigitalphotos.net

Having a slim waistline doesn't mean you have a healthy BMI

Measuring Your BMI

The body mass index is measured by taking the weight, measured in kilos, and dividing it by the height, measured in metres, squared. There are many calculators online that will do the calculation for you.

The result tells you whether you are underweight, healthy, overweight, obese etc. Those who have a BMI of 18 or lower are considered to be underweight. To be healthy, you need a BMI of between 18.1 and 24.9. Anything higher than that and you are overweight and above 30 you are classed as being obese.

This chart is for adults only. When considering the BMI of a child, the age will also be considered, among other factors. This is to help with a growth chart and not the regular body mass index chart that adults use.

Limitations of the BMI Chart

For the average adult, the BMI is ok to use. By average, I mean someone who does up to the recommended amount of exercise per day, is of good health and not pregnant. Anyone who doesn’t fit into the average person will find that the BMI isn’t quite accurate.

One of the major problems is that it only takes a general measurement of the health. This doesn’t consider whether that weight is from muscle or fat. While one pound of muscle weighs the same as one pound of fat (of course they weigh the same!), the muscle will be denser than the fat. Muscle naturally weighs more if you took them to be the same size.

The BMI chart doesn’t take this into consideration. Someone could weight more than is considered healthy but that doesn’t mean that it is all fat. I remember a paratrooper being told that he needed to lose weight because he was considered obese by the BMI scale – there wasn’t an inch of fat on him! It was pure muscle!

There are many athletes and sports players who will be considered obese on the scale. Some will have some fat on them but the majority it is all muscle. The calculation just fails to take this into account.

Now going the other way, where someone is considered underweight. My sister found that this happened – she used to dance six days a week for four or five hours per day. She ate my parents out of house and home but the doctors consistently told her to put on weight because she was underweight according to her BMI!

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A Healthy BMI Doesn't Means Someone Is Healthy!

Just because someone has a healthy BMI does not mean that they are healthy. Something that the scale fails to take into consideration is the distribution of the weight. Someone may have a healthy BMI but if their excess fat is around their abdomen, they are more at risk of obesity problems than someone whose excess fat is around their thighs or arms.

This is because around the abdomen is where all the major internal organs are. More pressure is placed on these organs and the fat stops them from working properly.

When considering your health, it is important to think about your body shape. Those who are more at risk have an apple shape. The abdomen fat is the hardest to get rid of but it is important that you try very hard for your health.

The BMI scale also fails to take other health issues into account. Someone may have a healthy weight but that doesn’t mean the rest of their body is healthy! Likewise, someone may be overweight but that doesn’t mean something is wrong with them – in fact, pregnant women should be ‘overweight’ due to their growing baby.

Finding a Healthy Weight that Looks Good

Someone who is at the top of their healthy BMI scale shouldn’t just think that they’re healthy so they can stop trying to lose weight. At the same time, the lowest on the BMI scale won’t necessarily look good. It is important to find a weight where you look and feel great (if you look great, you’re more likely to boost your self confidence and esteem).

Many health professionals recommend that you aim for your BMI to be between 21 and 23. This is in the middle of the healthy scale and where most people look good. Going too low could make you look like a skeleton, while going too high means that you risk putting on a little weight and going back over your healthy weight.

Is the BMI Scale Really Effective?

The BMI is great for the average person but it is not something to solely rely on. You need to take into consideration whether your higher weight is because of fat or whether it is mainly muscle. There is no point in relying on the BMI scale purely for your health. There are many other factors, including other ailments and conditions or whether you are pregnant. However, if you are trying to lose weight, this is a good scale to help determine when you can think about stopping.



Jun 20, 2013 2:03pm
I think you have highlighted important limitations regarding the use of BMI. However, it is important to recognize that the majority of the limitations are due to people using BMI inappropriately e.g. in athletes. BMI was not designed for such populations. Furthermore, there is considerable evidence linking BMI to numerous chronic diseases including cardiovascular disease and type 2 diabetes in general adult populations. As you say, BMI is not an all-encompassing measure of health, but it also should not be dismissed in the majority of adults; particularly due to it's simple calculation.
Dec 21, 2013 9:06pm
Nice analysis of the BMI, I agree with the limitations you pointed out.
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