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April 4, 2024

Is BMI Outdated? An Analysis of Body Mass Index and Health

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Bmi outdated metric

As someone who treats people with obesity, one needs an objective way to measure the risk of diseases associated with a person’s weight. To make a precise diagnosis and provide treatment recommendations for disease risks associated with a given weight, one needs to assess whether the measured weight is truly reflective of underlying metabolic issues. Currently, we use body mass index (BMI) as that measure. BMI calculation allows us to place one into a class of obesity and distinguish whether someone is overweight or obese.

BMI as a standard has been used since the 19th century. Recommendations for weight loss medications are often tied to this ratio of weight to height. Organizations such as the NIH encourage the general public to know their BMI. They may wish to discuss it with their healthcare provider, both in terms of their weight and their risk factors for heart disease and other related conditions.

It is helpful to know how BMI serves you and your patients as a measurement. It has been criticized as outdated and overly simplistic. Here, we will look at its benefits, limitations, and some possible alternatives.

How Did BMI Become the Standard?

BMI divides a person’s weight in kilograms by their height in meters squared.

It is classified in stages based on World Health Organization guidelines:

  • Underweight ≤18.5
  • Normal weight 18-24.9
  • Overweight 25.0-29.9
  • Class I obesity 30.0-34.9
  • Class II obesity 35.0-39.9
  • Class III obesity BMI ≥ 40.0

A Belgian statistician, Adolphe Quetelet, devised the measurement in the 1830s. He was attempting to define the body type of the “average” person. So, how did it become a standard measurement of health practitioners?

Without other metrics, doctors began using charts based on height and weight after the example set by Quetelet. One chart was devised for men and another for women.

They remained in use into the 20th century, but according to the American Medical Association, BMI took hold in the 1990s.

It proved a handy benchmark for prescribing some of the newer weight loss treatments on the market. It served as a quantitative benchmark for who was eligible for medications or bariatric surgery. It began to be promoted to the public as a motivation to watch one’s weight for health reasons.

BMI in Modern Obesity Medicine: Is BMI Outdated?

Benefits of BMI

BMI offers certain benefits that make it useful. It is easy to calculate, and it does not require special equipment. This makes it easy to assess during an office visit, moving directly to diagnosis and treatment recommendations.

Another benefit is that it’s familiar and easy to understand for the general population. People can calculate it themselves or easily find a BMI calculator online.

Those benefits aside, BMI has some drawbacks.

Limitations of BMI

There are several disadvantages to using BMI to determine obesity.

First, it does not account for body type. It does not measure muscle mass or bone density. For example, a person with high muscle mass, such as a football player, may be mistaken for having obesity, and a person with small bones but higher belly fat may be considered to have a healthy weight.

BMI does not account for ethnic variations in body size and fat percentage. Recall that it was developed by a Belgian, using presumably white subjects of European heritage. This population may tend toward proportions of fat to muscle and bone that differ significantly from other populations.

Following Quetelet’s narrow sampling technique, in 1994, the World Health Organization and the National Institutes of Health set obesity guidelines based on data from European and Caucasian Americans.

As a result, this data did not account for other races or ethnic groups globally because no data was available. In 2004, guidelines were set for people of Asian heritage using data from Thailand, China, Hongkong, Singapore, and Korea. However, South Asian, African, and Middle Eastern people were left out.

Importantly, BMI follows faulty logic. While someone carrying an unhealthy amount of weight may have a higher-than-recommended BMI, the opposite does not automatically hold.

The misuse of BMI can be harmful.

A paper published in the British Journal of General Practice suggests, “[BMI] is not only overly simplistic, such a glib understanding can be harmful to the health of a significant proportion of our patients.” It could lead to dismissing risk factors of heart disease, for example, or to someone trying to lose weight when they don’t need to.

Alternative Metrics of Obesity

Fortunately, alternative metrics for assessing body weight can be used in combination with other health data (including BMI).

Body Fat Percentage

Body fat percentage recommendations are tailored according to sex and age. The simplest way to measure it is with skin calipers. The calipers pull the fat away from the muscle to measure its thickness.

Usually, measurements from two or three places are used in conjunction. Caliper measurements are prone to human error, especially when conducted by someone other than a medical professional.

Patients may come in having measured themselves with calipers or been measured at a place like a gym or wellness clinic. It’s a good idea to help them understand what the measurement means.

Patients may also use home body fat scales.

These send a small electrical current through the body and measure how it moves through different types of tissue. It then calculates muscle, fat, bone, and water.

The result is a rough estimate at best. It can help a patient track changes to their body over time, but should not be used as an absolute measure of health.

Waist Circumference or Waist-to-Hip Ratio

Another consideration is waist circumference. If a person carries more fat around their waist compared with their hips, they’re at greater risk for heart disease and type 2 diabetes. Waist circumference can be considered alone or, for better context, related to hip circumference and body type.

A paper published in Nature Reviews Endocrinology argued that waist circumference is underutilized as a vital sign in clinical practice. The authors recommended that “decreases in waist circumference are a critically important treatment target for reducing adverse health risks for both men and women.”

As should be apparent by now, any one measure could have limitations when used in isolation. Whichever metric or metrics a clinician chooses, it’s advisable to take a holistic and individualized approach to obesity assessment, possibly integrating multiple metrics.

The Role of Obesity Medicine Specialists in Evolving Metrics

We at OMA believe in the importance of obesity medicine specialists in advancing the understanding and measurement of obesity.

Our members can play a role in researching and advocating for more accurate and comprehensive assessment tools. You can stay informed of the latest discussions about obesity measurement by getting involved or attending our conferences.

Much work remains to be done to produce more accurate BMI guidelines that can be applied to more people across America and worldwide. Consider joining OMA and taking part in the conversation about the evolving field of obesity medicine.

Humphreys, Stephen. The unethical use of BMI in contemporary general practice. Br J Gen Pract. 2010 Sep 1; 60(578): 696–697. doi: 10.3399/bjgp10X515548

Ross R, Neeland IJ, Yamashita S, Shai I, Seidell J, Magni P, Santos RD, Arsenault B, Cuevas A, Hu FB, Griffin BA, Zambon A, Barter P, Fruchart JC, Eckel RH, Matsuzawa Y, Després JP. Waist circumference as a vital sign in clinical practice: a Consensus Statement from the IAS and ICCR Working Group on Visceral Obesity. Nat Rev Endocrinol. 2020 Mar;16(3):177-189. doi: 10.1038/s41574-019-0310-7. Epub 2020 Feb 4. PMID: 32020062; PMCID: PMC7027970.

Article reviewed by:

Pankaj Rajvanshi Headshot 200x200

Pankaj Rajvanshi, MD, FAASLD, DADOM

Dr. Rajvanshi is a Board-Certified Gastroenterologist, Hepatologist, and Obesity Medicine expert, who practices in the Greater Seattle area. He also serves at the Chief Clinical Officer at FusioncareAI, an obesity care startup and advises Healthswim, a patient engagement platform. He obtained his medical degree in India and then spent 5 years at Albert Einstein College of Medicine, NY in liver research and clinical training followed by training in GI and Transplant Hepatology at University of Washington, Seattle. He currently does inpatient specialty medicine.