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  • Writer's pictureAnya

Should you be worried about your BMI? (A Dietitian’s Perspective)

Updated: Jun 17, 2021

Do you care about your Body Mass Index (BMI) results? Too bad because I don’t…

After six years of professional practice I’ve lost count of the number of clients who come to see me because of their BMI results.

Sometimes too low, and almost always too high, many of them worry about their BMI score like it’s a death sentence... and they’re always surprised when I’m not bothered by it.

Because, once you dig a little deeper, you’ll find that the BMI is a terrible predictor of the amount of fat you have in your body, and an even worse predictor of your overall health (by the way if you don’t know what a BMI is, visit this link).

In fact, it’s hard to believe that doctors or even some nutritionists use them at all.

Here are some reasons to not bother about your BMI. After you read them, I hope you’ll give yours the place it deserves: The bin.

1. It’s based on an outdated 19th century mathematical formula

Adolphe Quetelet was a 19th century astronomer, mathematician and statistician. He is also the inventor of the BMI mathematical formula.

Notice how I didn’t list “doctor” (or physician as they were called) in his credentials? Well, that’s because he wasn’t one.

Quetelet invented the BMI because he believed that mathematics could help him define the proportions of the ideal man. Anything which would deviate from that norm was abnormal.

He was not interested in tackling the problem of obesity from a medical point of view - which considers a person's individual circumstances - but from a mathematical and sociological one.

Because of this approach, Quetelet’s formula is inaccurate from a physiological perspective and outdated since we’ve now made progress in understanding how the body works.

Should we blame Quetelet for the BMI? Maybe, but since the man himself said that it should not be used to determine the level of fatness in an individual, I think I’ll give him a pass.

2. No, the BMI is not a direct measure of your fat

Thanks to the dieting industry, when most people think of weight they only think of fat.

And, since BMIs tag people as underweight, overweight, obese etc, it’s a common mistake to think that your BMI score measures the amount of fat in your body. It does not!

The BMI equation takes your height and weight into account. But it cannot pinpoint what makes up your weight.

To understand this, think of your body as a container filled with many things like muscle, water, fat, bones, organs etc… all of these together make up your total weight. And all of these, affect the score found in your BMI results (and your weight on the scale as well).

Medical professionals have known this for years and many have criticised the BMI’s inaccuracies. And yet, I keep getting patients whose doctors have told them to “lose weight” because of a slightly higher than average BMI. And unfortunately that includes children even when BMIs are not applicable to children.

I suppose that the temptation of using an easy “one-size-fits-all” formula to assess a person’s health is so strong for some, that they throw common sense out of the window.

I wish that health professionals would consider the individual context for each person, and the psychological stress of making someone obsess about their BMI before making a big fuss of it.

3. According to the BMI, many of the world’s best athletes are overweight

What do Usain Bolt, Michael Phelps and Lebron James have in common (other than a full trophy cabinet)? Yep, you guessed it, a higher BMI than what is considered healthy.

Athletes often find themselves on the higher end of the BMI index because as I mentioned above, BMI scores cannot differentiate the different elements which make up your body weight.

For example, muscles weigh more than fat. So, if you’re an athlete you’ll probably have more muscle than the average person, and your BMI may fall in the “overweight” category. Does that mean you are unhealthy? No.

2.3lb of fat vs 2.3lb of muscle

Photo source:

Athletes are a great example to illustrate why the BMI index is a bad indicator of your overall health. It's common for a person who exercises intensively, and eats healthy, to have a BMI which falls in the overweight range or obese range (25-29, and 30 or above respectively) to be healthier than a person with a “normal” BMI score (20-25).

Luckily professional and semi-professional athletes are usually well informed about their nutrition needs - though some doctors misinterpret their BMI scores - and they tend to not pay too much attention to a high BMI.

But what about an amateur sportsman?

Every month I see very healthy people with a regular sports routine coming to me in a panic because of a slightly high BMI reading. Often, they’ve drastically changed their diets and increased their training leading to less results and, in some cases, health problems linked to nutrient deficiencies. All that because of a random test they did on the internet or bad advice from a doctor.

4. It’s… kind of racist and sexist

Remember our friend Quetelet and his quest to find the ideal man? Well, his standards for perfection were based on the average Belgian male (Quetelet’s country of origin). And that’s it. No women, and nobody from other parts of the world!

If a methodology to assess someone’s health were done in the same way today, there’s no way it would be accepted as gospel as the BMI is. Especially since the consequences for this omission are real.

Since the BMI is used as an indicator of your overall health (risks for cardiovascular disease, diabetes etc…) doctors sometimes stop at a person's BMI and may either ignore other indicators of poor health, or tell someone to lose weight because their high BMI puts them at risk.

For example, Asians of Indian descent (which make up more than half of the Mauritian population) have a higher percentage of body fat even with BMIs which fall in the “normal range” and are at a higher risk of diabetes as a result.

Women too fall victim to the judgement of the BMI. When Quetelet devised his formula, he didn’t take into account the fact that women, by nature, have more body fat than men.

The healthy range for an adult women varies between 21-34% body fat while for a man it varies between 7-22%. Because the formula doesn’t consider this, the BMI will give the same value for a woman and a man who are of the same weight and height.

So if the BMI is not good for assessing your overall health, what is?

A more reliable measure than the BMI

I use waist measurements and body composition scans in my practice to help me assess the overall health of my clients.

These methods are more accurate and tell me exactly how much fat you have, what your muscle to fat ratio is, and they help me offer individualised nutritional advice.

So, if your BMI is too high, please do any of these tests before freaking out.

I) Waistline Measurement

Research shows that measuring your waistline is a better predictor of the amount of visceral fat (the type of fat that you need to control) in your body, and your risk for type 2 diabetes, high cholesterol, heart disease, and high blood pressure.

According to the UK’s NHS, the following waistline measurements are a sign that you should try to lose weight:

  • 94cm or more for men

  • 80cm or more for women

Consulting a health professional is advised if your waistline measurements are:

  • 102cm or more for men

  • 88cm or more for women

How to measure your waistline

  1. Follow the image above and place your measuring tape at the bottom of your ribs and at the tip of your hips. Make sure the tape is right in the middle of these two parts of your body.

  2. Breath out and let your body relax into a natural position (don’t pull your stomach in).

  3. Measure and compare your readings with the range in the image below.

II) Body Composition Scans

I will choose body composition scan results over the BMI anyday because it gives me a better picture of what’s going on in your body.

Body scans tell me the following about you:

  • Your fat to muscle ratio

  • How healthy your muscles are

  • Where fat and muscle is carried in the body

  • Your body fat percentage, water percentage, bone mass, metabolic age and more…

In other words, they give a more complete picture than the BMI ever will. By doing one, you’ll help your dietitian or doctor devise an individualised health plan that works for you and you'll know exactly how you are progressing with your health goals.

For example, I once had a client come to me completely disappointed because after two months of healthy eating and exercise, her BMI has not changed at all! One quick body composition scan revealed that she had in fact gained 6.1kg of muscle and lost 6kg of body fat (which is what you should be losing).

That 5-minute body scan changed her outlook and potentially stopped her from giving up on her effort to be healthy (if you’re interested, you can book one here).

What’s the lesson to take from this? That your weight tells you nothing about how healthy you are. So stop torturing yourself by checking your weight on the scales every morning and putting your trust in the BMI equation. Instead, switch your mindset to focus on your health and wellbeing, and the results should follow.

Why your health matters more than your weight

I hope the points above give you plenty of reasons to distrust the BMI. Personally, I’d like to go one step further and see it completely disappear from the fitness and medical professions (a girl can dream…).

One of the main reasons for this, is that the BMI makes the wrong assumption that weight=health. This is simply not true!

Every week, at least one person will walk into my consultation with a normal BMI but a nutrition assessment will reveal a high risk for certain chronic diseases, which is usually confirmed with a blood test. And, as mentioned earlier, some will have a high BMI and be perfectly healthy.

Remember, the BMI is a statistical model which completely ignores the individual circumstances of a person. It reduces us to a number and makes you forget that you are unique and that your mental and physical health will always be more important than how you look.

It places people into categories and perpetrates the notion that your health is based on your weight and when that happens, it invites all sorts of problems like under eating, fad diets, bingeing on protein supplements and all the things we torture ourselves with, just to shed a few kilos.

The truth is that if you eat a balanced diet and stay active, you’re likely to be healthier than someone who rarely exercises, but barely eats to keep their BMI down. Yes, even if your BMI is higher.

In other words, don’t worry too much about your BMI… Because I won’t.

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