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BMI – Bogus Measurement Index. Time to get real on fat.

Have you been told that you’re obese or overweight and know that it can’t be right? I have.

Last year, during a routine primary care check-up, one of the clinical assistants measured my height and weight. It was mid-spring, and I was in pretty good shape at the time. In fact, I had just gotten a DEXA scan (It’s a body fat measurement that we will explore later.) as part of a health evaluation. It was a stellar 9%. I was feeling good!

I was 6’3” and 200 pounds and had recently scored a favorable 9% body fat. As the medical assistant left the office, she handed me a sheet of paper that focused on achieving and maintaining a healthy body weight. Wait…what? This can’t be right? How am I overweight? You know the answer. BMI – Body Mass Index, or as I like to call it Bogus Measurement Index! BMI attempts to quantify the muscle, fat, and bone in an individual, and then categorize that person as underweight, normal weight, overweight, or obese based on that value.[1]

BMI is old school. Think rotary phone vs. iPhone 7. AND research[2] shows that BMI regularly overestimates “obese-ness” in athletes, or those with more lean muscle mass, especially those that participate in strength training on a regular basis and have low body fat percentages. In fact, many pro athletes would be deemed as obese or overweight if BMI was the sole measure of body composition and health risk classification[3]. LeBron James, at 6’8” and 238 pounds, would be classified as overweight with a BMI of 26.1. Clearly, the scale is flawed. HA!!!!

So why do healthcare workers use it? It’s easy. It’s cheap. It only requires height and weight. In my practice, as an exercise specialist, we collect BMI for the exact same reason. It can work well in large populations when it’s necessary to assess health on a broad scale. For example, one study surveyed older adults in the USA – 57.4% of the 60,000 involved were overweight, obese, or morbidly obese (using BMI) and had a lower physical quality of life than their leaner counterparts.[4] Without BMI, this data would have been laborious and expensive to collect!

Since my main focus with patients is disease prevention and lifestyle change, I never classify health risk using BMI alone. Alternative methods exist to determine body composition. Using body fat percentage is a better indicator of overall health, especially when we know where the fat is located.

For example, the more belly fat one has, the greater the risk[5] for:

  • Cardiovascular disease
  • Insulin resistance and type 2 diabetes
  • Colorectal cancer
  • Sleep apnea
  • Premature death from any cause
  • High blood pressure

This means that HOW you measure body fat is important; and there are myriad methods. I believe that using one of the four methods listed below is best. Each is different, but using one of these will provide more useful information vs BMI!

  1. Bioelectrical Impedance (BIA) – You’ve undoubtedly seen these on digital scales from tech giants like Fitbit and Withings. An electrical signal passes quickly through water that is present in hydrated muscle tissue but meets resistance when it hits fat tissue. This resistance (impedance) is measured to help calculate body composition. Depending on the monitor, body fat percentage is provided in less than 20 seconds.
  2. Skin Fold – Some people call this “the pinch test." Taking a skinfold measurement is a common, but often uncomfortable, method for determining body fat percentage. Skin folds are a two-compartment model, in that there is a separation of adipose tissue from muscle, then measuring it, to determine body fat in an individual. Accurate measurement technique is important. Find someone that’s experienced, as the more the practitioner has done, the more consistent and accurate the data.
  3. Bod Pod – It’s like stepping into a giant egg. Bod Pod is a shorter, more pronounceable name for air displacement plethysmography that calculates lean and fat tissue. The Bod Pod measures body mass (weight), calculates body density, and determines body fat and lean body mass.
  4. Dual-Energy X-ray Absorptiometry (DEXA) – The gold standard and my preferred method of body composition measurement. DEXA scan registers fat and lean mass distribution throughout the entire body in 7 to 10 minutes. It’s capable of detailing overall fat mass, as well as regional, fat mass, lean mass, and bone density.

Once you know your body fat percentage, it’s easy to determine what “classification” you fall into. The first table, adapted from Jeukendrup and Gleeson[6], gives a rough estimate of body fat percentages for men and women.

Males Females Rating
5-10% 8-15% Athletic
11-14% 16-23% Good
15-20% 24-30% Acceptable
21-24% 31-36% Overweight
>24% >37% Obese

This data changes a bit when adjusted for age, as you can see in the second table, also from Jeukendrup and Gleeson[6]:

Age Up to 30 30-50 50+
Females 14-21% 15-23% 16-25%
Males 9-15% 11-17% 12-19%

Here’s the bottom line on body composition and fat: get a second opinion if your BMI results don’t pass your personal “sniff test”. Find a wellness facility that performs different types of body composition testing. The gold standard is going to be DEXA, but it’s also the most expensive. As long as you’re being tested consistently (same time of day, same nutrition and hydration status, preferably before strenuous exercise), the changes you see will be accurate.

If your BMI is worrisome, and the second opinion validates that data, it’s time to up the workout intensity and incorporate strength training and perhaps some interval training to torch calories during your workouts, and even more so at rest. And it’s time to consider changing your diet. Get smart. Don’t let an old-fashioned equation get you down – harness the power of data and make sure your hard work in the gym is paying off!

**Wait! The Athletic-Minded Traveler research team recently came across a new way to look at body composition - tri-ponderal mass index (TMI). TMI scores (mass divided by height cubed) were more stable with age and estimated body fat percentage versus BMI z-scores in adolescents (R2=0.64 versus 0.38 in boys and R2=0.72 versus 0.66 in girls), according to researchers at the University of Alabama at Birmingham. [7] What does this mean? Well, perhaps BMI is headed out the door. More research needs to be done on the topic, but TMI is hardly too much information. It's a step in the right direction!**

[1] "Body Mass Index." Wikipedia. Wikimedia Foundation, 29 Mar. 2017. Web. 03 Apr. 2017.

[2] Tomiyama, A. J., J. M. Hunger, J. Nguyen-Cuu, and C. Wells. "Misclassification of Cardiometabolic Health When Using Body Mass Index Categories in NHANES 2005 2012." International Journal of Obesity 40.5 (2016): 883-86. Web.

[3] Chen, Angus. "If BMI Is The Test Of Health, Many Pro Athletes Would Flunk." NPR. NPR, 04 Feb. 2016. Web. 02 Apr. 2017.

[4] Bottone, F. G., Jr., K. Hawkins, S. Musich, Y. Cheng, R. J. Ozminkowski, R. J. Migliori, and C. S. Yeh. "The Relationship between Body Mass Index and Quality of Life in Community-living Older Adults Living in the United States." J Nutr Health Aging 17.6 (2013): 495-501. Print.

[5] "Belly Fat in Men: Why Weight Loss Matters." Mayo Clinic. Healthy Lifestyle, 28 Apr. 2016. Web. 02 Apr. 2017.

[6] Jeukendrup, Asker E., and Michael Gleeson. Sport Nutrition: An Introduction to Energy Production and Performance. Champaign, IL: Human Kinetics, 2010. Print.

[7] Peterson C, et al "Tri-ponderal mass index vs body mass index in estimating body fat during adolescence" JAMA Pediatrics 2017; DOI: 10.1001/jamapediatrics.2017.0460.

Athletic-Minded Traveler Editor Daniel Gaz authored this blog post.


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