Ever went to the doctor and they told you that you need to lose weight because of your BMI? Let’s talk about the validity of BMI.

You were probably taught how to calculate your BMI in health class. You also might have had the different BMI categories drilled into your memory. But how accurate is it?

What is BMI?

BMI or body mass index is a measure used currently to diagnose if someone is underweight, “normal” weight, overweight, or obese. From there, it’ll be used to estimate someone’s risk for diseases. How is BMI determined? It’s a ratio of someone’s height to weight. That’s it. Two different variables. It doesn’t include physical activity levels, nutrition status, environmental factors, genetics, socioeconomic status, history or current food insecurity, nada. BMI solely focuses on height and weight.

The Development of BMI

In the 1830s, Lambert Adolphe Jacques Quetelet was investigating how to find “l’homme moyen,” or the average man. Lambert was a Belgian statistician, sociologist, astronomer, and mathematician. I’ll make a note here that he was not a physician.

The data BMI was based off of was from a sample group of white, European men. There were no women or people of color included in the studies to develop BMI.

Something else to note is Lambert explicitly stated that BMI could not and should not be used to indicate the level of fatness in an individual. So, 200 years later, why are we still using it?

8 Flaws of BMI

Racial Bias
The subjects involved in the development of BMI were a group of white, European men. There weren’t any people of color. So, with the development of this tool, it assumes everyone should have the same genetic makeup as someone who is white.
There are many studies that have shown people of color on average have different body composition makeups compared to white people. One of the biggest flaws is that the sample group was a poor representation of the entire human race. If we’re using a tool and applying it to everyone, shouldn’t the data collected to develop the tool reflect an accurate representation of the people it’s being applied to?
Assumes Health is Equivalent to Body Size
There are two pieces of information that are used to determine BMI. Someone’s height and their weight. That’s it. BMI is used very commonly as a diagnostic tool. There is also a strong assumption made about someone’s behaviors and health status just by their BMI. One of the best elements of healthcare and being able to provide individualized care is to take all the pieces of the puzzle into account. The large emphasis on BMI (aka height and weight) is robbing patients of receiving the best care possible.
Discrepancies between Men and Women
So circling back (*cue cringe corporate jargon reaction*) to whom the sample group of participants consisted of for BMI - all the participants were men. Women and men have very different body composition breakdowns. Women carry more fat in their hips, butt, and breasts. Men have larger shoulders and smaller waists. The body composition distribution is completely different. But the development of BMI didn’t include any participants that were women. So when we look at BMI and the different categories, we’re looking at what a “normal,” white man might be categorized as. Yet, BMI is pushed onto women all the time.
Doesn’t Factor in Age
Our bodies change as we age, it’s no secret. There have been some studies indicating that older adults have different BMI specifications compared to young adults. If someone were older and intentionally trying to lose weight, this could result in loss of muscle mass, not fat mass.
Excludes Muscle Mass, Bone Mass, Water Weight, etc.
Going back to the basics, as if I haven’t hammered this in your head enough, BMI only includes height and weight. Nowhere does the calculation include muscle mass, bone mass, water weight, waist circumference, or ratio of fat mass to muscle mass. All of these data points sound like key components that should be included if we’re actually trying to get a well-rounded picture of someone’s health when solely looking at physical features. A professional football player who is the same height and weight as a man who works a 9-5 and leisurely works out will have a completely different body composition makeup as this man. But BMI will claim they have they’re categorized the same. BMI takes surface level information to evaluate health when there is so much more that goes into it.
Over-Reliance on BMI leads to Dismissal of Serious Health Conditions
Time after time again, I’ll hear stories as a medical professional that a patient went to the doctor for something and came out being told to lose weight. From going in with a sore throat to a headache to knee pain to digestive issues, you name it. This isn’t to say all doctors preemptively recommend weight loss because that isn’t true. There have been too many stories that I’ve heard and other dietitians have heard about this. If you google “fatphobia in healthcare” you’ll find plenty of stories. It’s very important to hear the stories from the people who experienced it themselves, don’t just take my word for it.
BMI Criteria Changed in 1998
The BMI criteria actually changed within the past 30 years. In 1998, the “normal” BMI range changed for both men and women. The upper limit for a “normal” BMI for women used to be 27 and for men it used to be 28. It was reduced to 25 for both men and women in 1998. Overnight, millions of people became “overweight.” One of the most interesting things about this change is that the decision to change the BMI criteria was based on a report that was funded by pharmaceutical companies that made weight loss drugs. So essentially people who would benefit from people being told they need to lose weight were the ones funding the report that changed the BMI criteria to include more people in the “overweight” category. Seems like a conflict of interest, right?
Insurance Charges Higher Premiums for High BMIs
One of the last flaws about BMI is some insurance companies have charged higher premiums to people with higher BMIs. So, looking at the different flaws above, it’s evident there are a couple if not a many holes in the validity to utilize BMI to the extent we use today. While healthcare in the U.S. already has financial obstacles surrounding it, the influence of BMI on premiums only exasperates the current issues and situation.

What Should We Use Instead of BMI?

So given BMIs numerous flaws and outdated history, healthcare could benefit from a pivot away from BMI. To provide the best individualized patient care, we need to look further than height and weight. Some physical data characteristics we can review are body composition, waist circumference, and waist-to-hip ratio. To get an even more in-depth picture of the patient’s case, we should review lab values, a dietary recall, history of or current food insecurity, history of eating disorders, and socioeconomic status - just to name a few.

The reason BMI is used so much is honestly because 1) it’s cheap and 2) it’s fast. All you need is a calculator, scale, and height measuring tool. And it takes less than one minute to calculate BMI. It’s disappointing how often money is a driving factor to decisions being made, not just exclusive to healthcare.

Our healthcare has progressed exponentially over the past two centuries, so our diagnostic criteria should also progress as well. There’s too strong of an emphasis on BMI and we need to go beyond it for the sake of our patients.

Here are some of my favorite resources to unlearn fatphobia in healthcare and embrace a more weight-inclusive approach.

Bottom Line

If you’ve ever felt shamed for your BMI, that’s a flaw in our healthcare system and you shouldn’t take it to heart. There are many inadequacies in the validity of BMI as a diagnostic tool and we need to have that discussion more. BMI is one piece of data to the entire puzzle that is someone’s health.

Want to hear more? Check out The Up-Beet Dietitians podcast episode on why BMI is Bulllsh*t.

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