what is bmi

What Is BMI? Here’s How Body Mass Index (Supposedly) Works

What is BMI? BMI stands for Body Mass Index and it’s basically a ratio of a person’s height and weight. Specifically, BMI is the number that is generated after dividing someone’s weight in pounds by their height squared in inches and then multiplied by 703. A Belgian mathematician developed the ratio in 1832, noting that it should be used as a statistical generalization for large populations (in other words, not intended for individual use).

But, what has BMI become?

BMI has become the main way that we measure overweight and obesity in this country. You know all those stats about how we’re all doomed to die in a fatpocalypse? They’re all based on this bogus “BMI” measurement.

Here are the Categories of BMI:

CategoryBMI range - kg/m2BMI Prime
Very severely underweight:less than 15less than 0.60
Severely underweight:from 15-16from 0.60 to 0.64
Underweight:from 16 to 18.5from 0.64 to 0.74
Normal:from 18.5 to 25from 0.74 to 1.0
Overweight:from 25 to 30from 1.0 to 1.2
Obese Class 1: (moderately obese)from 30 to 35from 1.2 to 1.4
Obese Class 2: (Severely obese)from 35 to 40from 1.4 to 1.6
Obese Class 3: (Very severely obese)over 40over 1.6

As you can see in the BMI chart above, there are several categories for BMI – including the one we’re all meant to strive for: “normal” or “healthy weight.”

So, BMI is the way we measure obesity and overweight in this country EVEN THOUGH we do not have good reason to believe it measures health. Is this sad and detrimental to our health? Yes and I’ll explain why below.

BMI: So, how did this b.s. measurement gain popularity?

bmi funny

The BMI’s popularity is due to a paper published in the July 1972 edition of Journal of Chronic Diseases by Ancel Keys, which, purportedly, found BMI to be a good proxy for body fat % among height-to-weight ratios. Keys, like the Beligan polymath who developed BMI, did not see at useful for individual cases.

But, lo and behold, the National Institutes for Health (NIH) decided to use BMI as its measurement and, in 1998, a committee decided that they should lower the BMI cutoff for “ideal/normal” weight, which effectively made 25 million Americans “overweight, ” and thus “unhealthy,” overnight , 3 members of the committee responsible for making the recommendation had direct ties to pharmaceuticals that manufactured diet pills for profit.

A fourth member was the lead scientist for the program advisory committee of Weight Watchers International.” Did these Americans, in fact, go from healthy to unhealthy overnight? That’s not as easy to answer as you might suspect. While I want to say, “of course not!” I also know the power of persuasion and stigma to have strong effects of people. In other words, if you are told, overnight, that you became sickly and unhealthy – will you believe it?


What BMI is not:

  • a measure of health
  • a measure of worth

BMI: So…what’s the problem?

  •  BMI has no causal relationship to a person’s health! In fact, there are studies that show those who are overweight tend to have LOWER mortality than those who are normal- and underweight!
  • BMI has become something that is considered SO important (read: profitable), students are now being sent home with “BMI report cards” showing where they stand on this measurement
  • BMI has become something so important (read: profitable) our government has waged a war to get people to lose enough weight to become “normal” on the BMI chart. Unfortunately, we view weight in this country as something that can be easily fixed (the weight loss industry is, after all, a $6B industry!). You won’t see anyone telling you that you can change your HEIGHT (though, I imagine this will occur soon enough with the latest eugenics-like invention that will sure enough come to market when weight loss “cures” stop selling).
  • BMI has become something so important (profitable) that local states, government agencies and employers are encouraging citizens to lose body weight (i.e. points from their BMI). For instance, “MI Healthier Tomorrow” is a communications initiative of the Michigan Health and Wellness 4 x 4 Plan that is designed to encourage Michiganders to lose 10 percent of their body weight. How wonderful! 
  • When the media discusses the obesity “epidemic,” it often uses footage of “headless fat people” (see above) – in other words, they typically use footage of very large persons’ bodies to show us the extreme cases of obesity (BMI) and to remove us from feeling implicated in this crisis. The truth is – most of us ARE indeed a part of this crisis! Brad Pitt and Will Smith are overweight based on BMI. Should we incentivize them to lose 10% of their body weight? I am overweight. Yes, by 10 pounds, but, alas, I am implicated in this crisis by virtue of having a healthy no-longer-bulimic body
  • We are so obsessed with weight and weight loss that we have sacrificed our health and many of us, including medical doctors, are under dangerous assumptions about what health “looks like” and weighs. (walking, etc) This affects people who are thin and malnourished but fall in the “normal” BMI range as they are often assumed to be healthy and engaging in healthful behaviors. Alternately, people who are overweight (per BMI) and in good health and engaging in healthful behaviors may be told they need to lose weight. Do you see the insidious nature of this weight obsession? Even those who are healthy may be told to engage in dangerous and unhealthful practices simply because they land in the overweight category, which the zeitgeist believes is bad even when science shows us that it tends to be more predictive of health!

Is BMI just a weight to height ratio?

So, remember, this entire CRISIS hinges on some bullshit measurement of weight-height ratio that is NOT a measurement of health. And, remember, all of us with bodies are implicated in this EPIDEMIC. You never know, tomorrow the NIH can decide that “normal BMI” should actually be dropped a couple of points and, overnight, YOU can be a diseased drain on society.

*Related: Top 10 Reasons Why The BMI Is Bogus

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