Why is BMI inaccurate and misleading?

The Big Problems with BMI: Inaccurate, Outdated and Discriminatory

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In the spirit of helping you to arm yourself with sound knowledge against diet culture and the emotional and physical damage it can inflict upon us, in this post I’m going to cover an important and and insidious topic: BMI. Namely, I’ll be addressing the many problems with BMI, such as:

  • Why BMI is misleading
  • Why is BMI not a good health indicator
  • Why is BMI still used
  • What to use instead of BMI as a measurement of health

You may have heard time and again that a “high BMI increases your risk for certain diseases such as heart disease, high blood pressure, type 2 diabetes, and certain types of cancers”, blah, blah, blahhhhh. But what if this wasn’t necessarily true? In the same way that body weight and the number on the scale are not predictors of a person’s health status, you’ll see that measuring health by a controversial number like the BMI is not just inaccurate, misleading, and outdated, but focusing on it can cause more harm than good. Is BMI outdated? Is BMI racist? What’s wrong with BMI? Keep reading to find out the answers to these questions, and to free yourself from this number, and the bias it perpetuates, forever!

Why is BMI bad
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OK, so first things first, what exactly is BMI? BMI stands for Body Mass Index, a measure of weight adjusted for height, and calculated as weight in kilograms divided by the square of height in meters (kg/m2). The purpose of this measurement is to determine an individual’s “fatness” (whatever that means), by categorizing people into risk groups according to their BMI number. These categories are then used to determine “risk factor” with respect to the development of, or the prevalence of, several health issues. As we’ll see later on, health status not as simple as calculating a math equation. To better understand the many problems with BMI, let’s take a look at how it became such a mainstream, yet misleading, measurement of health status.

A brief history of BMI

An important point when considering why are BMI measurements controversial and inaccurate is how this index came to be. First off, BMI is outdated, literally. This measurement was developed by Adolphus Quetelet in the mid 19th century based on the observation that body weight was proportional to the square of the height in adults with “normal” body frames. Now here’s where it starts to get messy. Quetelet was a “Belgian mathematician, astronomer and statistician, who developed a passionate interest in probability calculus that he applied to study human physical characteristics and social aptitudes”. Quetelet was not a physician, nor did he study medicine. And yet, we continue to use his mathematical formula to predict health status. This is just one of the many problems with BMI measurements (or Quetelet’s Index, as it was known before), as we’ll continue to see.

In fact, Quetelet never intended that this index be used to measure an individual’s health or wellness at all. He used it to determine “the ideal” man. In his book A Treatise on Man and the Development of His Faculties, he writes the following: “If the average man were completely determined, we might consider him as the type of perfection…And everything differing from his proportion or condition, would constitute deformity or disease…or monstrosity.” Nice ?. Oh, and his study population consisted of white, European men. No women. Just wanted to emphasize that.

Skipping a bit ahead, in 1972, it was physiologist Ancel Keys who reintroduced the tool as the BMI, and the medical community has since used it as a standard measure of individual health for the general population. This decision was largely influenced by a study on “fatness” that Keys undertook, using mostly data from white European and American men (once again). In the study, Keys looked at about 7,400 men from five European countries and analyzed their fat-body density and subcutaneous fat thickness, two measures of body weight, but not a reliable measure of health status.

Another interesting and important characteristic that renders the BMI misleading and inaccurate is that in the late 20th century, health and life insurance companies adopted the BMI to replace their own height-weight tables. These tables, btw, were based on data drawn from mostly white men and some white women. Also, height-weight tables were not intended to determine health; they were meant for the purposes of determining what to charge prospective policyholders. This data was, for the most part self reported, and collected by sales agents, not health professionals. However, it became increasingly common for doctors and other health professionals to use insurance companies’ height-weight tables in order to “measure health” in individuals. This practice was later replaced by the use of the BMI.

Why are BMI measurements controversial?

In this section, we’ll take a closer look at the main problems with BMI, and how continuing to use this index as a way to asses, diagnose and make recommendations for health conditions can be at great odds with the main responsibility healthcare practitioners have been entrusted with: first, do no harm.

What are some criticisms of only using BMI as a measure?

BMI has come under criticism lately because it doesn’t provide a full picture of a person’s health. Research, such as this paper, also addresses that relying on BMI alone to predict a person’s risk of health problems can be misleading.

First off, as this research paper points out, “it is increasingly clear that BMI is a rather poor indicator of percent of body fat. Importantly, the BMI also does not capture information on the mass of fat in different body sites”. And let me just add right here one of the most harmful problems with BMI, as we’ll see below. This marker is based on the paradigm that body fat is equal to disease, which is deeply flawed.

This obvious flaw in the BMI measurement means that it it can’t distinguish between muscle tissue, bone tissue or any other tissue in the human body! So, let’s say, a person who has lot of muscle mass as a result of weight bearing exercise, for example, will probably have a high BMI score. Can BMI alone tell me that this person is at a higher risk of heart disease or diabetes? Of course not! Among the many other factors that play a role in a person’s health, BMI does not take into account genetic predisposition, lifestyle, or access to medical care, to name a few.

As with respect to what BMI is really based on (ie. what Quetelet considered to be a “normal” body frame), let’s take a look at how BMI is not only inaccurate, but is deeply rooted in discrimination. This index fails to consider that body types vary greatly throughout different ethnic groups–and that’s just how nature indented it to be. Let’s check out why BMI is inaccurate and misleading…and stigmatizing.

Is BMI really accurate? TLDR: No.

Is BMI really accurate?
As a “measurement” of health, the BMI is outdated and full of blind spots

As we’ve just seen, the BMI was derived from a formula based solely on the size and measurements of French and Scottish male participants. In other words, BMI was devised exclusively by and for white Western Europeans men. This type of health marker is just not appropriate for women and people of other ethnicities. For example, when compared to white Europeans of the same BMI, Asians appear to have a four percent higher total body fat. Does that mean that this group of people is “less healthy”? Of course not! As this paper concludes, “the relationship between BF% [body fat] and BMI is ethnic-specific. For comparisons…between ethnic groups, universal BMI cut-off points are not appropriate”. Relying on this method to determine health may even lead to misdiagnosis and mistreatment, especially in women and in other ethnic populations. Let’s dig in even deeper into the problems with BMI…

Is BMI racist? Yes.

Another significant flaw in using the BMI to determine an individual’s health status lies in it’s racist roots. As we just saw above, this index was designed to measure weight in different populations using data from European white men. As discussed in this article from Today’s Dietitian, “Experts say the BMI perpetuates the idea that the often-thinner bodies of whites are the standard to which everyone should be held and are therefore superior to the often-larger bodies of persons of African descent”. 

As a Latina, I have experienced the oppressive and false belief that something was wrong with my body since I was very young. Back in the 1990s when I was in middle school in the US, part of the physical education program required the kids to be measured, weighed and have fat fold measurements taken (in front of all the other kids??‍♀️). I remember the shame I felt at 11 years old and being told that, in comparison to my thinner, white classmates, I had “too much body fat”. Needless to say, this kick-started body anxiety and an eating disorder that lasted a few years into my teens. And all because there’s an impossible weight standard that society determined we must all contort to. For more on westernization, body image and eating disorders, check out this publication.

BMI doesn’t take into account body composition, physical activity level, body type, age, genetics, cultural diversity, access to health care services, socioeconomic status or ethnicity. It’s really just another number, like body weight, that doesn’t tell us anything about a person’s health status.

The widespread use of the BMI index as a standard of health contributes to enact biases and discrimination that are harmful to marginalized people. For a better look into how “medicine’s over-reliance on the BMI may be actively harming our health”, check out this excellent article on the racist roots of BMI by Your Fat Friend.

Additional BMI limitations

Why is BMI not a good health indicator?
We’re not all supposed to be the same size…and there’s nothing wrong with that!

So why do doctors and other healthcare providers still use BMI? Well, it’s widely considered to be an “inexpensive”, “quick” and “easy” tool to “asses modifiable risk factors”. And it’s been used for such a long time that it’s still believed to be the best tool for this we’ve got so far. As we’ve just learned, it’s not that simple. In this next section, I’ll discuss two other problems with BMI that continue to perpetuate weight stigma and anti-fat bias: the “fat=disease” paradigm and the existence of metabolic health in individuals in larger bodies.

Fat isn’t a disease

To me, the biggest of all problems with BMI is that is assumes that “fat=bad”. To start off with, I highly recommend that you check out this video on size diversity to get a feel of why a weight and fat-centric approach to health is based on false assumptions and can do more harm than good.

Another major complication that arises with over relying on BMI as a health marker is that this number alone can also affect your healthcare. For example, your doctor may feel obligated to give you (sometimes unnecessary) additional health screenings, prescribe certain drugs, and require additional follow-up appointments due to a high BMI number. Therefore, your BMI may be unfairly tied to your healthcare costs in the case that you are otherwise metabolically healthy. Within marginalized and low income populations, this can be especially detrimental.

I really love and constantly refer to this article from the Nutrition Journal by Dr. Lindo Bacon and Dr. Lucy Aphramor that addresses, and ultimately debunks, the following assumptions that underline the conventional and harmful “fat is a disease” health approach, such as:

  • Adiposity poses significant mortality risk
  • Adiposity poses significant morbidity risk
  • Weight loss will prolong life
  • Anyone who is determined can lose weight and keep it off through appropriate diet and exercise
  • The pursuit of weight loss is a practical and positive goal
  • The only way for “overweight” and “obese” people to improve health is to lose weight
  • “Obesity”-related costs place a large burden on the economy, and this can be corrected by focused attention to “obesity” treatment and prevention

The article discusses various arguments that question these long held weight and health beliefs, and makes a strong case for the following findings:

  • Health benefits associated with weight loss rarely show a dose response (people who lose either small amounts or large amounts of weight tend to get the same health benefits). ??‍♀️
  • It is not known whether, or to what extent, the health benefits can be attributed to the weight loss itself or changes in health behaviors.
  • Methodological problems, which tend to bias the studies toward showing successful weight loss maintenance.
  • Association is not causation. “Obesity” is associated with increased risk for many diseases, but causation is less well-established.
  • The association between weight and health risk can be better attributed to weight cycling (repeated cycles of weight loss and regain) rather than “fatness” itself.

And this is just the tip of the iceberg! Attributing a body size (that exists in nature among many other body sizes) to disease is not just dehumanizing, but also promotes and perpetuates weight stigmatizing behaviors.

If you’re interested in learning more about how health is much more than body size (as the current diet culture has us believe), and diving into how socioeconomic inequalities and biases are huge determinants of health, I highly recommend these books by the authors of the above study:

Body Respect: What Conventional Health Books Get Wrong, Leave Out, and Just Plain Fail to Understand about Weight

Health At Every Size: The Surprising Truth About Your Weight

“We really need a much more sophisticated, nuanced discussion that’s going to help people to be healthier, and it’s really quite damaging when we make assumptions based on BMI…There are a lot of other ways to help to figure out whether or not people are healthy that give us much more valuable information than BMI ever can about health.”

Dr. Lindo Bacon

Metabolic health vs BMI

Another factor that the BMI measurement doesn’t take into account is metabolic health. As a Health at Every Size aligned practitioner, I do believe that you can be healthy at any size, and even at any BMI number, since that’s what we’re covering here. Which brings us to a very common question that gets asked frequently: Does metabolically healthy “obesity” exist? Yes, and as an example, this paper talks about how there are many “exceptions to the paradigm of ‘more fat means more metabolic disease’, and the subjects in this condition are referred to as metabolically healthy “obese’ [quotation marks are mine] (MHO)”.

Per the paper, so far we have no accepted criteria for identifying MHO individuals, however, most studies suggest the definition of MHO to be “obesity” without the presence of metabolic diseases such as type 2 diabetes, dyslipidemia or hypertension. As this other paper states, “approximately 10-25% of ‘obese’ [quotation marks are mine] individuals are metabolically healthy most likely due to preserved insulin sensitivity. Recent studies suggest that inflammation of visceral adipose tissue, ectopic fat deposition and adipose tissue dysfunction mediate insulin resistance in human obesity independently of total body fat mass”.

The authors also recognize that the metabolic conditions often found in some people in larger bodies may involve “mechanisms beyond a positive caloric balance such as inflammation and adipokine release”. I say we start by investigating deeper into how health disparities and weight stigma are involved in the development/poor management of these very conditions, rather than blaming the fat tissue. What do you think?

Another example of more problems with BMI comes from this study that looked at more than 40,000 people across all population groups and reported that more than 30 percent of people in the normal BMI category are cardio-metabolically unhealthy based on their blood pressure readings and metabolic lab values such as:

  • Blood lipid levels: HDL (“good”), LDL (“bad”) cholesterol and triglycerides
  • Blood glucose levels
  • C-reactive protein ( a measure of inflammation)

In this same study, nearly half of people considered “overweight”, and 29 percent of those considered “obese” were considered to be healthy on the basis of their health markers. Interestingly, the authors of this study estimated that as many as 74 million people who are considered to be “unhealthy” on the basis of their BMI are, in fact, healthy according to these other parameters. Just some food for thought. ?

What to use instead of BMI

What to use instead of BMI
Focusing on health promoting behaviors, such as your preferred choice of movement, is a better way to gauge health than BMI

As we’ve explored the multiple problems with BMI as a measure of health status, you may be wondering what to use instead of BMI. To answer this question, I firmly believe that the Health at Every Size approach can be highly beneficial. Instead of focusing on weight loss, diet culture and a narrowly defined and socially constructed body size, the HAES paradigm focuses on sustainable health promoting behaviors, self respect and self acceptance. It is a paradigm focused on empowering people in terms of their health and wellbeing, regardless of shape, size, age, race, ethnicity, gender, dis/ability, sexual orientation, religion, class, and other human attributes. 

Here are some great areas you can focus on for supporting your health that does not include body size or BMI. This is also a good list of options for practitioners to work with their clients, according to what their actual health needs are:

  • Gentle nutrition and intuitive eating
  • Healing your relationship with food and your body
  • Joyful movement, as you choose to participate in it
  • Emotion and stress regulation
  • Mental health support
  • Self care
  • Access to health care
  • Adequate diagnosis and management of medical conditions (instead of prescribing, or being prescribed, weight loss from the get go).

Conclusion

I hope this information has helped you to understand that numbers related to body size such as BMI and body weight can’t determine who you are. They are also inappropriate for determining how to best care for yourself. If you have been a victim of body size stigma and this has negatively impacted your relationship to healthcare, the HAES community has an amazing registry of HAES aligned professionals you can search for by specialization and your physical location. Just click the button below:

And now I’d love to know your thoughts on the many problems with BMI! Please let me know your questions, comments or any feedback on this topic below in the comments section.

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