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11 Great Reasons To Pretend BMI Never Happened

According to my calculations, BMI is questionable at best.

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Body Mass Index (BMI) is a calculation that (allegedly) tells you if you're underweight, normal weight, overweight, or obese.

@bennymac_ / Via instagram.com

Maybe you've had a doctor or trainer calculate your BMI in order to give you some context for your weight in relation to your health. Or maybe you've calculated it yourself. You can even find your BMI yourself using a handy online calculator! But should you? In 2009 the American Heart Association issued an advisory about BMI and its limits in providing useful or reliable information on weight-related health risks, and a 2009 study found that BMI overestimated obesity in African American populations.

So, BuzzFeed Health reached out to Dr. Holly Lofton, director of the Medical Weight Management Program at NYU Langone Medical Center, and registered dietitian Brian St. Pierre, director of performance nutrition at Precision Nutrition, to get their expert opinions on the BMI, it's uses and limits, and whether or not we should pay any attention to it at all.

1. BMI is a weight-to-height ratio that's used to categorize people by body mass.

@keystoslim / Via instagram.com

It's considered an indirect measure of body fat because it's not actually a measure of how much fat is on your body. It's simply an equation that has been found to get a number that is, as the CDC notes, "moderately correlated" with more direct measures of body fat (more on how that was found to be the case in a sec).

Doctors and healthcare professionals use BMI because direct measures of body fat, while more precise, are technically sophisticated and expensive, and typically only available in labs and research settings. On the other hand, BMI takes just a quick calculation.

2. You get your BMI by dividing your weight in kilograms by your height in meters squared.

dribbble.com / Via dribbble.com

So, for someone who weights 150 pounds (or 68kg) and is 6' (or 1.82m) tall, the equation would look like this:

OR

68 / 1.82*1.82 = 20.5

A BMI of 20.5 puts you in the "normal weight" range according to the BMI categories. You can check out BMI tables to see all the other ranges.

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3. But here's the thing: BMI wasn't developed to assess individuals' health or even their body fat.

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The ratio itself was created by a mid-19th century mathematician and statistician whose project was to identify the measurements of the "average man," which, as a mathematician, he set out to do by plugging in measurements and finding average values and normal distributions.

It only became known as the Body Mass Index when, in a 1972 study, an obesity researcher named Ancel Keys published his findings on which of the weight-to-height ratios in current use produced results that best correlated to his own findings of body fat percentage in more than 7,400 men. He found that the mathematician's formula of body weight divided by height squared (which Keys named: Body Mass Index), was preferable to the others ones he tried.

Before long epidemiologists were using it to study health in populations. In 1985 the NIH recommended using it as a "simple and convenient" method of calculating body fat for both public health studies and clinical practice. And although BMI can be useful when looking at populations, it has some significant limitations.

4. BMI's most obvious limitation is that it can't discriminate between body mass that comes from muscle and body mass that comes from fat.

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For example: People with a good deal of muscle mass might have a BMI that puts them in the overweight range when in reality their body fat percentage may not be that high. And on the other hand, Lofton says, "elderly persons who are portly but have low muscle mass might have normal or even low BMI scores," which means that BMI is underestimating body fat, and not flagging a potential health risk that should be followed up on.

This is important because what doctors really care about when it comes to health (with respect to weight) is adiposity, or how much of your mass is body fat, says Lofton, specifically how much you have and where you have it. The reason for this is that high percentages of body fat can be associated with some cardiac health risks.

5. What makes BMI useful for looking at population trends makes it a pretty poor choice for evaluating individuals.

Sally Tamarkin / BuzzFeed News / Via cdc.gov

Take that frequent exerciser who has a lot of muscle. The BMI tells them they're overweight when they're actually not. So, not useful. But when you apply BMI to populations, the significance of the occasional person who's more muscular than average gets "washed out" by the vast numbers of other people who are not highly muscular (because the majority of the population is in fact not more muscular than average). In other words, says St. Pierre, on the population level, BMI can be "a good proxy for body composition because most people aren't outside the norms." (In this case the norm is that higher body weight is associated with higher body fat.)

BMI also doesn't take into account age, sex, bone structure, ethnicity, or fat distribution. And all of these are important factors when it comes to understanding the relationship between a person's weight and/or fat and their health.

6. A better way for you to get some potentially useful health-related info about body fat is to measure your waist circumference.

@xsyl_kex / Via instagram.com

Having abdominal fat can be an indicator that you have visceral fat, or fat around your internal organs, says Lofton, which as BuzzFeed Health has reported, can increase your risk of diabetes, cardiovascular disease, and more.

To get your waist circumference, measure around the very top of your pelvis (on your bare skin) with a tape measure. A waist circumference of 35 or more for women and 40 or more for men is associated with increased health risks, says Lofton. This is a helpful, non-BMI way to gather some data about your abdominal fat.

7. But that said, you can't get a complete picture of someone's health from BMI or body fat alone.

@amplyemmy / Via instagram.com

Measuring your waist circumference might offer a nugget of useful information, but it's data that needs to be looked at in the greater context of your overall health and lifestyle, because while it's true that certain factors (like visceral fat) are associated with health risks, health and fitness aren't dependent on your size or your weight or even your body fat. "Increasing in fat mass does not always lead to increase in disease," says Lofton.

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8. For example, when doctors assess cardiac risk, they're not looking just at your weight.

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In fact, doctors are looking for signs of metabolic syndrome, which is a predictor of heart disease. Metabolic syndrome is the name for the group of factors that increase your risk of heart disease, diabetes, and stroke. Lofton says that doctors determine whether someone has metabolic syndrome not by using BMI or even body fat percentage, but by looking at five risk factors. If a patient has any three (or more) of them, they are diagnosed with metabolic syndrome, says Lofton.

They are:

1. Low HDL cholesterol

HDL is "good" cholesterol — it removes cholesterol from your arteries).

2. Elevated blood pressure

As in, your blood pressure is above 130/85, or you need meds to keep it reasonably low.

3. Waist circumference over 35" for women or 40" for men

Again, a large waist can indicate high levels of visceral fat (that is fat around your internal organs).

4. High fasting blood sugar

Elevated blood sugar could be an early sign of diabetes.

5. Triglycerides over 150
Triglycerides — fats in the blood — are a kind of cholesterol.

9. And if you're happy and healthy, there's no medical reason to lose weight.

@hun.e_e / Via instagram.com

Let's say you have a high BMI. Let's say that by average or normative standards you weigh "too much" for your height. Lofton says that if you feel good, you're happy, you're leading an active lifestyle and eating a healthy diet (which help prevent disease and increase your chances of living longer), and your labs don't show anything hinky with respect to those metabolic syndrome risks, there's no reason to try to lose weight or lower your BMI.

"The goal is a healthy lifestyle and reducing [your risk of disease]. I'm happy as long as you are," Lofton says.

10. When it comes to clinical weight management and obesity treatment, there actually is a newer tool that seems to be better and more holistic than BMI.

Alberta Health Services / Via drsharma.ca

It's called the Edmonton Obesity Staging System (EOSS) and it was developed by Dr. Arya M. Sharma, medical director of Alberta Health Services Provincial Obesity Strategy in Edmonton, Alberta, Canada, and Dr. Robert Kushner, medical director of the Center for Lifestyle Medicine at Northwestern Medicine in Chicago. It was proposed in a 2009 article in the International Journal of Obesity.

The EOSS takes into account not just height and weight but a patient's psychosocial environment — are they experiencing discrimination or inequities or other problems because of their weight? — as well as quality of life markers like mobility and other health problems. Basically, Lofton says, it helps healthcare providers get a comprehensive look at a patient's life, health, and happiness, so that they can make informed and personalized recommendations for treatment. In fact, a 2011 study concluded that EOSS "may offer improved clinical utility in assessing obesity-related risk and prioritizing treatment."

Although Sharma is using it in his practice, EOSS is not recognized by the NIH as a standard of measure, says Lofton, and it's not used by most practices in the United States.

11. In conclusion, unless you're conducting a study about weight trends in large populations, feel free to disregard BMI, which can be a total life ruiner.

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BMI's usefulness is questionable not just because of it's limitations when used by individuals, but also, St. Pierre says, because relying on numbers and measurements can play into a self-defeating mindset where you feel like you are those numbers, and those numbers predict your happiness or success or your ability to make the changes you want in your life or body.

"It's just a data point, nothing more, nothing less," says St. Pierre, which is why he doesn't use BMI in his practice with patients.

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