BMI is still widely used to determine health risk and to categorize people according to their body size. But I haven’t used BMI as a metric since forever, because I think it’s incredibly faulty.

The truth is, that while BMI has been used for decades as an indicator of someone’s health and risk for disease, it’s actually a pretty weak measure. When I hear that a potential client’s BMI is high, I immediately put that fact into my back pocket and start looking at other indicators, such as bloodwork, diet history, activity level, and weight history, to name a few. 

Your health can’t be boiled down to ONE single indicator, especially your body mass index. Nope. 

What is BMI?

BMI was invented in the 1830s by a Belgian mathematician as a measure of the degree of obesity for populations during the war. Apparently, it was used to allocate resources (as in, if there are a lot of fat people in one place, they didn’t deserve to get as many resources as an area with more thin people. Uh…that’s troubling). 

The fact that BMI is now used on individuals is crazy, because the guy who invented BMI specifically said that it shouldn’t be used in this way. So why do we continue to do it? Don’t we have other measures of health and wellness? We definitely do, and while BMI can be used to detect patterns in someone’s weight, it shouldn’t be used as the sole indicator. 

So put down the BMI calculator and charts; here are my reasons why I think BMI is a poor indicator for health:

It doesn’t account for body type or composition

Some people are just bigger, some are smaller. Isn’t nature wonderful? We can’t all be the same size, but just because you were born with a larger body frame doesn’t mean that you’re unhealthy. BMI would disagree though, because plenty of people who weigh heavy because they’re just, well, big people – will clock in at ‘overweight’ or ‘obese’ even though they’re actually not. By the same token, having a high ratio of muscle to fat is also liable to put you into the ‘overweight’ category. Muscle weighs more than fat, and if you’re solid and muscular – think athletes or weightlifters – BMI won’t recognize that; it will just categorize you as overweight when you’re not.

Although NIH states that the BMI is an estimate of body fat, that’s not really a valid conclusion.

I’m sort of confused as to how a weight for height equation can even predict what someone’s body fat is. To confound things further, women generally have a lower BMI than men, but also naturally have more body fat – but BMI doesn’t account for gender differences. No bueno.

It doesn’t account for where fat deposits are in the body

Belly fat is more dangerous than, say, thigh fat, but if you truly have a greater ratio of fat to muscle, BMI isn’t going to tease out where that fat is located. 

It also doesn’t account for people who are overweight and healthy, or of low weight and unhealthy – again, it shouldn’t be the only indicator for assessing a person’s health. 

The categories within the BMI chart are troubling.

Underweight, Normal, Overweight, Obese. See anything wrong?

The use of the word ‘normal’ to describe someone’s weight in a population setting is obtuse. Normal for who?

What if I’m born in a bigger body, and I’m ‘normally’ categorized as ‘overweight’ by the same chart? Does that mean there’s something wrong with me? My actual ‘normal’ weight isn’t really ‘normal’? Even if it’s normal for ME?

By categorizing people into meaningless groups, the BMI chart does a great job of perpetuating weight stigma.  

BMI is very frequently wrong, where health is concerned.

And since BMI is supposed to be all about the health of the subject, this is a problem.

A 2016 study found that where BMI showed an ‘overweight’ result, nearly half of those people were actually cardiometabolically healthy. On the other hand, 30% of the people who came in as ‘normal’ on the BMI scale were found to be cardiometabolically unhealthy. The scientists took BMI and held it up against other indicators of health, such as glucose and cholesterol levels, among others. BMI just didn’t prove to be reliable. When health insurance companies use BMI as an indicator of health – and as a basis for fees, this is a huge issue. 

This study’s result means that 54 million people could be classified as ‘unhealthy’ when in reality, they’re not. That means they pay more, in money and possibly in psychological health as well.  

I can’t talk about BMI without giving a special mention (and I mean ‘special’ in a bad way) to the very harmful and fucked up practice of schools sending kids home with letters about how their BMI is too high.

BMI and Covid-19.

BMI has repeatedly been cited as a risk factor for covid-19. In other words, fat people are more likely to have worse outcomes from covid than people of ‘normal’ weight. 

This is what I have to say to that:

People who are fat may have an increased risk of covid, if their immune systems are weakened.

A larger body may be more difficult to intubate or ventilate. And perhaps most concerning is that overweight and obese individuals are less likely to be taken seriously or treated appropriately when they present to a healthcare professional or hospital with symptoms. (and here) This can not only impact the person’s outcome, but it also discourages them from seeing a doctor until they’re very unwell.

There’s a huge disparity in terms of weight, income, and lifestyle. In other words, people who are of lower socioeconomic status have a higher risk of becoming obese. The reason for this is multi-pronged, but involves social determinants of health that then impact their lifestyle. 

They have less access to healthcare, and less access to preventative habits like fresh food and gym memberships. They sometimes live in close quarters with many other people, or work low-paying jobs in environments where their risk for catching covid is higher. 

All of these make a difference in both the risk for catching covid, and your outcome if you do catch it. So yeah, no sh*t the outcomes are worse. 

There are other ways to determine a person’s health and disease risk without using BMI. 

Their overall diet.

Their lifestyle, and this includes emotional stuff, too.

Genetics, personal, and family history.

BMI may have been considered useful at one point, but it’s time we stop relying on it for health outcomes. At this point, it looks like BMI does more harm than good. 


Next read: The Biggest Loser: Why Are We Still Watching Weight Loss TV?