The Drawbacks of Using BMI to Measure Health

Woman weighing herself on a scale

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Body mass index or BMI is a calculation that determines weight status in adults by using your weight and height. The end result tells you if you're underweight, at a healthy weight, overweight or obese. A body mass index:

  • Over 40 is considered morbidly obese
  • Over 30 is considered obese
  • Between 25 and 29.9 is considered overweight
  • Between 18.5 and 24.9 is considered a healthy BMI
  • Under 18.5 is considered underweight

You can easily calculate your BMI by entering your measurements into an online calculator.

The Drawbacks of Using BMI

The BMI formula is so simple, it's easy to use by just about everyone. However, it's that simplicity that makes it inaccurate because it only takes into account your height and weight. Whether you're overweight or not requires much more information than just your height and weight.

Here are all the things that this BMI formula can get wrong:

  • How Much Muscle You Have: The more you have the higher your BMI will be, even though you may be healthy
  • Frame Size: A person with a big frame will have a higher BMI, although he or she may still be healthy
  • Gender: At the same BMI, women will usually have more body fat than men
  • Age: At the same BMI, an older person will usually have more fat than younger adults
  • If You're an Athlete: At the same BMI, athletes will usually have less body fat than people who aren't athletes.

If you're very muscular, pregnant, or have a large frame, your BMI calculation may show you as overweight or obese, even when you're not.

How your body fat is distributed is also important for predicting your risk of heart disease, obesity-related illnesses, and death. It's a good idea to use a variety of tools to determine how healthy your weight and body fat is including waist-to-hip ratio and/or your body fat percentage.

Is BMI on Its Way Out?

BMI has been a useful research tool on large populations because it is so easy for researchers to obtain the measurements necessary for computing BMI. However, its usefulness when applied to individuals has come into question. 

There's definitely a call to get rid of BMI as the only measurement of a person's weight status, and perhaps some day insurance companies will do so. More importantly, when you and your doctor are assessing your current health status today, there's already no reason to rely on BMI alone. Talk to your doctor about taking other factors into account, like your activity level, your frame size, your waist-to-hip ratio and your body fat percentage.

The findings suggest that about 34.4 million Americans are considered overweight based on BMI and that 19.8 million are considered obese. Which is just crazy!

A Word From Verywell

As mentioned above, BMI doesn't take into account all of the factors that make us healthy. What's even more disturbing is that many companies in the U.S. use employees' BMI as a factor in determining their health care costs. So, a person with a high BMI may pay higher premiums, even though it isn't clear whether that person is genuinely overweight and unhealthy or not.

There's definitely a call to get rid of BMI as a way to measure health and weight and, because of this study, we may just see that happen.

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Article Sources

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  • Tomiyama, AJ, JM Hunger, and J. Nguyen-Cuu. Misclassification of Cardiometabolic Health When Using Body Mass Index Categories in NHANES 2005–2012. International Journal of Obesity (2016). Doi: 10.1038/ijo.2016.17. Web. 02 Feb. 09.