The limitations of body mass index (BMI)

 166608586A few days ago a friend on Facebook reposted a cartoon of a woman declaring that according to the BMI chart, she was too short. For those who aren’t familiar, Body Mass Index, or BMI, is a simple measurement tool used to calculate height-to-weight ratio.

Some people argue that BMI is too simple a measurement. Is BMI still useful for someone concerned about their weight?

“It can be helpful as one factor to consider in determining chronic disease risk in the general population,” explained Chelsea VanDusen, a clinical dietitian at Houston Methodist Hospital.

She explained that other factors such as age, gender, past medical history, family history and lifestyle factors including diet, smoking and physical activity levels all play a part in helping to determine risk and must all be considered in order to have an accurate picture.

The limitation of BMI as Chelsea explained it is that it’s intended as a “measure of fatness” but doesn’t actually take body fat percentage into account. “It’s therefore skewed in individuals who are highly muscular or those who have muscle wasting,” she said.

BMI doesn’t take body fat percentage into account, making it a skewed metric Click To Tweet

For example, a bodybuilder – whose weight may be higher than normal due to increased muscle mass – may appear obese according to his BMI number. In comparison, an elderly person’s BMI number may appear in the healthy range (<27) even though they’ve had significant muscle loss.

166596238“In fact, elderly people may have increased mortality risk with a BMI of less than 22, whereas that is considered in the ‘healthy range’ for younger adults,” Chelsea said.

Another limitation of BMI is the fact that it does not differ between men and women even though men tend to have larger frames in addition to a more muscular build. So even though a man and a woman may have the same BMI, the woman would likely have a higher percentage of body fat than the male.

BMI also doesn’t take fat distribution into account.  For example, a person’s waist circumference can be used to determine their amount of visceral fat, which is located around vital internal organs and is often associated with increased levels of inflammation and chronic disease risk.

Why do people continue to use BMI as a measurement to determine how healthy someone is?

“While other measures of body fat including waist measurement, skin-fold measurements and bioelectrical impedance are useful, they tend to be more expensive, intrusive and/or difficult to standardize due to human error,” Chelsea explained.  “Therefore, BMI continues to be widely used.”

Regardless of your BMI number, remember – it’s only one piece of the puzzle. And unless you’re planning on growing a few more inches, the best way to reduce it is by eating better and getting some exercise

Want to see what your BMI is? Try the calculator below:

Erik Noriega

Erik Noriega

Senior Editor at Houston Methodist
Erik Noriega has been writing words for almost 40 years and has been getting paid for it for more than 20. An almost-native Houstonian by way of Mexico City, he has also worked for the Archdiocese of Galveston-Houston and the Greater Houston Partnership.
Erik Noriega

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Erik Noriega

Erik Noriega has been writing words for almost 40 years and has been getting paid for it for more than 20. An almost-native Houstonian by way of Mexico City, he has also worked for the Archdiocese of Galveston-Houston and the Greater Houston Partnership.

  • Georges St. George

    I don’t understand how even using the NIH’s standards for BMI measurement are even considered reasonable. A male my height (5’8″), would have to be between 135 and 158 lbs. In reality, am not sure if this is even in the normal range; I am reasonably fit but not full of muscle and don’t even come close at 180 lbs — I am considered borderline obese by their (and my health insurance) standards. I don’t know anyone who is 5’8″ that is over the age of 21 that would fit in the “normal” range. I am not sure if it is possible for me to lose 22 lbs in a healthy fashion just to meet the minimum; I comfortably wear size 32 pants and medium shirts.

    • This is exactly what we talk about in the blog, @georgesstgeorge:disqus. BMI is more an estimate than anything else. A lot of individual factors come into play, so it shouldn’t be relied on as a definitive metric for one’s health. Thanks for sharing a comment. – Jason

      • Georges St. George

        Yes, I gathered that — good article — just curious why it’s even being considered in the first place by the NIH; I haven’t done a scientific study, but I don’t know very many healthy people that fit that standard. I know I’m healthy, but screening using their standards has implications for health insurance and even employment in some fields (in particular, law enforcement and military).

  • sheilzasmith

    Thanks for posting this great blog!!

    If you want to measure your correct weight then measure with BMI. It calculates correct body mass. It is available for all ages person. BMI measurement can often be found referred to in health and fitness articles and is used by the medical profession as one indicator of health.
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