You’ve probably heard the term body mass index, or BMI, which is commonly used as a measure of health. It calculates your height to weight ratio, thereby (in theory) determining whether you are overweight or underweight. The calculation goes like this: divide your weight in pounds by your height in inches squared (that’s your height multiplied by your height), then multiply that answer by 703. The number you get will fall into one of the below categories:
- Underweight (BMI below 18.5)
- Healthy weight (BMI of 18.5 to 24.9)
- Overweight (BMI of 25 to 29.9)
- Obese (BMI over 30)
These categories have been used to predict someone’s likelihood of developing chronic diseases, like type 2 diabetes and heart disease, for example. But BMI is flawed. BMI is based upon the average height and weight of Caucasians. Studies have shown BMI may under or overestimate body fat in different demographics, such as women or persons from different racial/ethnic backgrounds. For example, people of South Asian descent on average have smaller body frames and fat is distributed differently than for those of European descent. (In fact, they may develop type 2 diabetes at lower BMIs than people of European descent.) Age can deem BMI inaccurate, too. Young men generally have more muscle than body fat, while older adults have more fat and less muscle.
BMI isn’t just a number. Using a universal BMI chart can actually lead to misdiagnosing, not diagnosing, or over diagnosing someone with a health issue they may or may not have. This could also have implications regarding life insurance premiums, meaning segments of the population could be paying higher premiums unnecessarily.
How Did BMI Become A Measure Of Health?
BMI wasn’t initially created to be an indicator of health. Back in the 1830s, Adolphe Quetelet, a Belgian astronomer and math statistician, wanted to calculate the size of the average man using a population of Belgian men.
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It wasn’t until 1972 that Ancel Keys, an American physiologist, used BMI to estimate body fat percentage. Healthy BMIs were established using white policy holders’ longevity data from Metropolitan Life Insurance Company. In 1993, the World Health Organization (WHO) designated BMI ranges as underweight, healthy, overweight and obese using data from white people in Great Britain, ages 16 to 64.
But the data the WHO used differs from other data, which allows for more people to fit into a healthy BMI range. In fact, data from the National Health and Nutrition Examination Survey (NHANES) recommends a healthy BMI range up to 27.8 for men and 27.3 for women.
What Are Better Predictors Of Health?
Focusing solely on someone’s BMI can promote eating disorders—not to mention weight bias, where healthcare providers view obese patients as lazy. They may dismiss certain symptoms, telling patients they just need to eat healthily and exercise more often when really their symptoms are indicative of a deeper issue. While BMI can be valuable in some settings, it is better to take a holistic approach when looking at predictors of health, such as:
- Socioeconomic status and healthcare disparities. Those who don’t have access to or can’t afford fresh, healthy foods; who live in more polluted neighborhoods and who don’t have access to quality healthcare centers of excellence are more likely to develop health conditions.
- Activity level & lifestyle. People can be at a “healthy” BMI but it doesn’t necessarily tell the story of their lifestyle. If they smoke, if they’re not active and if they don’t eat a balanced, nutritious diet, they can certainly be less healthy than someone who is overweight but who regularly exercises, eats well and abstains from smoking.
- Genetic health history. Our health is partly environmental but also partly genetic. The health history of your parents can inform you of health conditions you may be at greater risk for in the future.
For a select group of people, BMI may be a part of a puzzle piece that tells the story of their health. But for a larger group of people, using BMI can actually be detrimental. As we learn more about disparities in healthcare, implicit bias and examine long-ago established, race-based healthcare guidance, we can correct issues so that everyone has an equal opportunity to reach their optimal health.
Kimberlydawn Wisdom, MD, MS, FACEP, is the Senior Vice President of Community Health & Equity and Chief Wellness & Diversity Officer for Henry Ford Health. Read more about Dr. Wisdom.
