This Is Why BMI’s Wrong About Ideal Body Weight

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This Is Why BMI's Wrong About Ideal Body Weight Title Graphic - In the background someone holds their hand up to the camera as if to say "Stop"

Hello Lovelies:

If I told you to take your weight in kilograms and divide it by your height squared, you’d probably look at me a little funny, right?

What if I said that the answer to that equation decided whether or not you’re healthy? Sounds bonkers, right?!

But that’s exactly what the Body Mass Index (BMI) does. The formula for BMI is weight in kilograms divided by height squared. And the results apparently decide whether of not you’re at an ideal body weight or unhealthy.

But that’s a vast oversimplification of a very complex subject. Health isn’t decided by something so simple. And it was never meant to be.

So let’s talk about it! Today we’re going to dive into why BMI doesn’t necessarily decide your health outcomes…

Weight Fluctuations And Graves Disease

Sara of sits on a log over the water. Her head is tilted back and her eyes are closed. She has a big smile on her face. Her experiences with Graves Disease and weight fluctuations showed her first hand that BMI alone can't predict health outcomes or healthy body weightIt’s me <3

As many of you know, I have Graves Disease. And one of the symptoms I experience during a flare up is weight loss. It happens quickly and it’s typically pretty noticeable.

Guess what happens when a flare up causes me to lose weight… I get so many complements! People look at my smaller body and assume this must mean that I’m healthy and doing great. My smaller size merits more respect due to our unfortunate societal norms.

But even though I become smaller and have a lower BMI, I’m unwell in this state and need medical help.

BMI and societal beauty standards on weight would assume that I’m healthier in my autoimmune hyperthyroid state.

A woman sits with her hands clapsed in front of her face. She looks exasperated. Perhaps at societal beauty standards and body weight obsessions

Treatment for my disease can make me gain weight. During my first flare up my doctors had to quickly fight the hyperthyroid aspect of my disease because my levels were high and my symptoms were out of control. This meant a high dose of medication and a lot of weight gain. If we go by BMI, I became “obese.”

The compliments stopped and the “concern” started. My larger body was now viewed by some as unhealthy. Something I needed to focus on and change for the sake of my well-being.

But, here’s the thing… I gained weight because I was finally being treated and on my way to getting better.

So, even though many unfortunately wouldn’t think it by looking at me, I was healthier when I had gained a lot of weight. I WAS focused on my health. Extremely.

Someone holds their hand up to the camera as if to say "Stop" Like maybe we should stop using BMI and societal assumptions about what a healthy weight looks like to judge someone's health

Related: Podcast Interview – How to Take Care of Yourself with an Autoimmune Disease with Sara Flanagan

The “concern” was painful and unnecessary.

And I have thin privilege… so imagine how exhausting, disheartening and horrible it must be for those who don’t?!

Everyone’s experiences are different. Our bodies are all different. And that’s not only ok, it’s beautiful. We need to stop judging each other’s bodies.

And part of that judgement comes from our societal beliefs on weight and health. BMI plays a large roll in that. So let’s dive into why BMI is BS.

1. BMI was Never Meant to Measure an Individual’s Health

A stop sign sits on an angle. In the background are leaves and a white fence. In this sense, we should stop using BMI alone to determine someone's ideal weight and health

The Body Mass Index was never meant to decide whether you’re healthy. It was actually created with the idea of community health in mind. Kind of like how Q-Tips were never meant to be used inside your ear – we’ve all been using BMI in an unintended way this whole time.

The mathematician who invented the body mass index, Adolphe Quetelet, created his formula almost 200 years ago to help the government decide how to allocate health funds to the general public. (source)

Instead of deciding if someone was at an ideal body weight, BMI was supposed to quickly measure the approximate health of a large population.

Even Ancel Keys, the scientist who popularized the use of BMI in the 1970s, stressed that BMI should be used to determine the health of a population, not individual people. (source)

A man looks at the camera and raises an eyebrow while looking skeptical

Clearly no one took Ancel’s advice…

Related: This Weight Watchers App Is The Worst (It’s For Kids?!)

The ultimate problem is that BMI oversimplifies an incredibly complex thing. You can’t decide if someone’s well just by looking at their weight and dividing it by their height squared. You can’t even look at someone and know everything about their well-being.

Which brings me to…

2. BMI Doesn’t Accurately Predict Health Outcomes

A woman brishes her hair back from her face and looks down at her phone. She looks dejected. Her shirt says "Guess." Kind of like how BMI guesses at ideal body weight without considering all factors.

Body Mass Index is so widely used to determine your health… but according to studies BMI actually shouldn’t be used as a way to measure body fat or to decide if you’re healthy. (source)

Why? Because health outcomes do not necessarily match up with your BMI.

While we’ve been taught to believe that falling into the obese category automatically means that you’re not healthy, that’s not exactly true. In this study, people who had a BMI of over 30 (obese) either experienced more health issues… or were healthier on average than those who, according to BMI, were at an “ideal body weight.”

It went either way. Showing that BMI outcomes are not accurate in determining your health.

But wait, there’s more!

A woman looks at the camera and places her hands on her temples, as if exasperated. She's standing in front of greens leaves.

This study found that those in the overweight category had lower mortality rates than those the Body Mass Index favoured as “normal.”

Does that mean that you should worry if you’re naturally in the “normal” category. No. The point is that your body will settle where it functions optimally at. We’ll talk more about that soon. But, essentially, everyone’s optimal weight is different. If you’re healthy and well, that’s what matters. And BMI can’t decide that for you.

5 friends stand together otuside to take a selfie. They are all different shapes and sizes. Everyone looks very happy. BMI alone can't decide their health outcomes or ideal body weight

We need to stop automatically assuming that where someone falls on the BMI scale determines their health, be it “normal” or not. And, since our collective knowledge of BMI and body size has informed our opinion on the health of those around us, we should also stop making assumptions about someone else’s health at a glance.

Fun fact, a new Canadian guideline states that obesity should not be defined by weight alone. Instead, it recommends that obesity is defined by someone’s health instead of just their weight. Needed change is coming baby!

Related: Working On Awesome Lifestyle Changes? Avoid These 5 Mistakes

3. BMI Guidelines Changed Overnight

Someone holds two hands up to the camera, covering their face. As if to say "Stop"

In 1998 the National Institute of health changed their BMI guidelines. Suddenly you were considered overweight if you had a BMI of 25 instead of 27.8. (source)

Overnight 29 million Americans went from normal weight to overweight.

Of course, this change in the BMI scale served to increase overweight and obesity numbers. And thus the “obesity epidemic” was now a bigger problem.

While the decision was in part to try to meet then standards of the World Health Organization, apparently they also felt 25 was an easier number to remember. (source)

A woman stands in fron of some large windows. She has her hands on her hits and stares down the camera with a confident look.

I don’t know about you, but that seems like a silly reason to classify someone’s weight as unhealthy to me.

And problematic changes continue to this day.

In 2013 the American Medical Association (AMA) passed a resolution that recognized obesity as a disease. Even though their own Committee on Science and Public Health advised against it (in a five page paper no less). (source)

The Committee stated that obesity has no actual symptoms and isn’t always harmful, which goes against the definition of a disease. And, as we already know, it can be protective for some and even sometimes lead to better health outcomes. (source 1, source 2)

A woman sits by a pool outside. She turns her head towards the camera and smiles.

The Committee also worried that labeling obesity as a disease may ultimately hurt people by adding to already prominent and problematic stigma. And by also increasing medical bias and leading to unnecessary treatments.

But the AMA decided to move forward with their resolution anyway. Further feeding into the unfortunate societal idea that BMI and obesity can accurately predict health outcomes. (source)

4. You Can’t Look At Someone And Know Their Health

3 friends stand together otuside to take a selfie. They are all different shapes and sizes. BMI alone can't decide their health outcomes or ideal body weight.

Fun fact, sumo wrestlers typically have low rates of heart disease and diabetes and tend to be quite healthy. They also happen to have larger bodies and a high BMI. (source)

BMI doesn’t take into account:

A woman poses for the camera. She had a big smile on her face and is dressed in a fashionable red top and grey pencil shirt with red pumps. She looks amazing!

This is a major reason why health outcomes do not typically match up with someone’s BMI. It’s an unreliable source that only looks at a tiny part of a very large picture.

When it comes to our bodies, one size definitely doesn’t fit all.

So there really isn’t any such thing as an overall ideal body weight based on height.

We’re are all naturally different. We also all fluctuate in different ways and for different reasons. And that’s ok! You are still worthy of the same love and respect always, no matter your size. And you can still be healthy if your body isn’t naturally whatever BMI tells you it should be.

Related: Why The Quarantine Fatphobia Needs To Stop

5. Weight Bias Affects Quality of Medical Care

A woman stands outside, in front of a tree. She stands with a hand on her hip and stares down the camera. Her expression is neutral.

Fatphobia and weight bias are problematic and prevalent forms of societal discrimination that reliance on BMI perpetuates. (source)

And it also affects medical care. (source)

Patients with a higher BMI are more likely to:

  • Receive less empathy from doctors
  • Be stereotyped by doctors as weak willed and/or lazy
  • Encounter more disrespectful comments from health care providers
  • Experience bias medical treatment

A woman sits with a white blanket draped over her head and overing her body. She gently holds the blanket with her right hand. And looks at the camera. She has a tough, frustrated expression - perhaps she's frustrated with BMI and it's obsessioin with predicting your ideal body weight.

This ultimately leads to poor quality of care and has a massive affect on someone’s well-being. 

Empathy from your doctor, for example, not only leads to better care, it also makes you more likely to follow their medical advice. Because you trust that they have your best interest at heart. Which ultimately helps you get better!

But those who don’t receive that empathetic care and, instead, experience fatphobia in their doctor’s office are less likely to follow their doctor’s advice. And they might not seek out preventative care in the future, for fear of experiencing the same hurtful treatment. (source)

Bias treatment also means that weight is sometimes blamed as the cause of unrelated health issues. Leaving the real culprit unexamined and untreated. And unfortunately that only leads to unnecessary and preventable suffering and pain. (source)

This is a whole lot of not ok.

6. “Normal” BMI Doesn’t Always Equal Healthy

A man and a woman stand under a tree. The show is from a low angle, so we look up at them. And they look up at the sky, each staring in different directions.

You can absolutely have a “normal” BMI and be healthy. But having a BMI that’s considered “abnormal” doesn’t necessarily mean you’re unhealthy.

We’ve already talked about a study that found that those in the overweight category often fared better than those BMI favoured as “normal.” And that those considered obese were sometimes healthier on average than those who had a “healthy weight” according to BMI.

And yet we still assume we can decide someone’s health at a glance based on their size. Or that we know what an “ideal body weight” would even look like.

There are a lot of factors that determine your body’s size. Many of which are completely out of your control.

This includes genetics and environment. And there’s even something called set point theory.

A woman stands on a rock as the sun rises in front of her. She lifts her arms in the air and faces the sunshine.

What’s set point theory?

Basically, it proposes that there’s a weight range that your body naturally wants to settle into. It’s part of your homeostasis. It’s completely different for everyone. And is the range where your body functions best at, so you can feel good and do your thang. (source)

Your body will fight to stay there, regardless of what a 200 year old mathematical equation has to say.

Societal standards blind us and make us judge each other. Which isn’t ok. You can’t look at someone and decide they’re healthy or unhealthy or that their body is good or bad.

A calculator sits on a grey backdrop - A 200 year old mathematical equasion can't accurately decide your ideal body weight or health outcomes.

All bodies are good bodies. And everyone deserves love and respect, regardless of their shape or size or what society has decided is currently fashionable and acceptable.

And regardless of what a BMI says.

Be kind. To yourself and others. We’re all beautiful as we are right now. And we need to stop judging each other’s bodies.

Related: 7 Uplifting Self-Love Lessons From A Graves Disease Diagnosis

Final Thoughts

A woman holds a cup of coffee and leans against a wall in a break room.

Health is a very complex thing affected by many factors. More than a simple mathematical equation could ever take into account.

We’re all very different. All of your bodies are different from mine. Your genetics and environment are completely different from mine. The exercise you enjoy, the food that makes you feel awesome, the stress relief activities that work for you… you guessed it; all different!

A woman stands outside and smiles, looking away from the camera. Her hand is on her heart and she looks happy. Freeing yourself from societal expectations and ideals about what consitutes a healthy body weight is so liberating.

What matters is that you feel well and are doing well. And if you’re not well, that you have access to the medical care you need to get better. Oh, and self-acceptance and self-love go an awful long way too <3.

There are a lot of things that work together to determine your well-being. But BMI and it’s obsession with determining your ideal body weight and theoretical health outcomes is not one of them. I propose we leave it behind with other outdated practices from the 1800s, like leeching and doctor’s not washing their hands (seriously).

What are your thoughts on BMI? Any outdated health practices or current wellness ideals you’d like to say goodbye to? Share your thoughts and experiences with me in the comments below.

Health and love,


Thought of the day: Some things are best left behind.


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Sara | Ms. Health-Esteem

Sara Flanagan is a wellness writer and the creator of, where she shares her story of being diagnosed with Graves Disease, a chronic autoimmune disease, and empowering herself to do everything she can to thrive in spite of her diagnosis. She writes articles on self-love, acceptance, wellness and nutrition. Join the Health-Esteem Family today and share in the journey.


  1. Reply

    Colleen Lanin

    August 7, 2020

    BMI seems like one of those things that was invented for life insurance companies to help them determine how likely it is you might die from obesity. It really doesn’t reflect your actual health. You could be a body builder and have a crazy high BMI.

  2. Reply


    August 7, 2020

    I love this. I’ve never put much stock in BMI for anything health related. Everyone’s BMI is different, and every BMI can mean something different.

  3. Reply


    August 7, 2020

    Great post. BMI isn’t the end-all, be-all of health. I think as long as you’re active and your bloodwork is good when you go to the doctor, you’re good. I watched a show the other day that talked about a BMI study that found that sumo wrestlers who have MASSIVE BMI’s and a huge amount of fat on their bodies are actually incredibly healthy because they are so active.

  4. Reply

    THE JOYOUS LIVING entertainment + disabled blogger (@thejoyousliving)

    August 7, 2020

    great post. with my illness i had put on a good 60+ pounds in a couple years and have had so much trouble taking it off thanks to medications and lack of ability to exercise. thankfully i’ve found doctors who don’t look at the BMI and scold me but encourage me. they know it’s only a small part of my issues.

  5. Reply


    August 7, 2020

    This was so interesting and so informative! Thank you for sharing this!

    cute & little

  6. Reply


    August 8, 2020

    I agree. BMI should not determine your overall health. There are so many more factors involved.

  7. Reply

    Charis | Choose Frugal

    August 8, 2020

    Health looks different for everyone and we never know what people are struggling with!

  8. Reply


    August 8, 2020

    BMI has been improperly used for so long. I am glad that this article addresses its fallacies and why it should not be the standard we are using!

  9. Reply


    August 8, 2020

    I hear you!
    I have actually been denied help with my body medicly because of BMI…

  10. Reply


    August 8, 2020

    This is so informative post, I had so many misconceptions about BMI and now I have a much clearer knowledge about it all.

  11. Reply

    Angela Ricardo Bethea

    August 8, 2020

    Very informative! I learn something new every and this definitely help me learn about BMI. Thanks for sharing!

  12. Reply

    blair villanueva

    August 9, 2020

    I never checked my BMI regularly coz it is misleading. I feel healthy and good the way I am 🙂

  13. Reply

    Ntensibe Edgar Michael

    August 10, 2020

    “The mathematician who invented the body mass index, Adolphe Quetelet, created his formula almost 200 years ago to help the government decide how to allocate health funds to the general public.”…, what? Is this for real? And we are even still talking about this, in this day and age?

  14. Reply

    Minakshi Bajpai

    August 10, 2020

    Wow, this is very very helpful, thank you.

  15. Reply

    katrina Kroeplin

    August 11, 2020

    i don’t like BMI’s either and never will. they arnet always right in my opinion.

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