BMI, or body mass index, is a hot topic. It’s used to categorize people based on their weight and height, and determines their diagnosis, treatment, and care. It is a one-size-fits-all approach to health that just doesn’t make sense for many body types.
Developed by a mathematician named Adolphe Quetelet about 200 years ago, this screening method for overweight and obesity in populations of white men was never meant to be used as it is today. So is there any value in determining or using BMI as an indicator of health? To find out, we interviewed Tom Kearn, exercise physiologist and sports medicine doctor, as well as registered dietitian Suzanne Kalmbach.
Meet the Expert
- Tom Kearn, DC, ICCSP, is an exercise physiologist and sports medicine doctor in New York.
- Suzanne Kalmbach, MA, RDN, is a registered dietitian.
What Is BMI?
“BMI is a formula that uses a patient's height and weight ratio in order to classify them into different health categories: underweight, healthy weight, overweight, obese in which each category has associated health risks,” explains Kearn.
A specific number range determines these categories:
- Underweight: less than 18.5
- Healthy weight: 18.5 to 25
- Overweight: 25 to 30
- Obese: over 30
Some charts call the healthy weight range normal weight, while some include a category for extremely obese that starts at a BMI of 40.
How to Calculate Your BMI
To calculate your BMI, use this formula: BMI = kg/m2.
Kg is your weight in kilograms, and m2 is your height in meters squared. There are also plenty of calculators that will do the math for you, such as the one from the National Heart, Lung, and Blood Institute, which allows you to input your data in standard or metric measurements.
Does BMI Really Matter
“BMI indicates an individual's weight for their height, not taking into account muscle or body fat. Excess weight can be a contributing factor to common diseases, but it is only one piece of the puzzle,” says Kalmbach. Other factors to consider include diet, exercise, hereditary influences, stress levels, and more, which can significantly influence overall health.
Several groups of people shouldn't use BMI, as it fails to accurately represent their health even more so. These include:
- Athletic and muscular people
- Long-distance athletes
- Anyone who is pregnant
- Elderly adults
“BMI is just one factor out of many to consider when monitoring your overall health. But it is helpful to know your BMI so you can be cognizant of various health conditions like type 2 diabetes, cardiovascular issues, and high blood pressure that could occur in the future if a person is overweight or obese,” says Kearn.
Your BMI screening shouldn't be the only factor to consider when determining your health, but it can point you in the right direction to better understand where your health is at and where it needs to be.
Why BMI Is Controversial
“BMI isn’t an accurate representation of health because it takes the ratio of height and weight and doesn’t factor into account the type of weight a person may have, such as muscle compared to fat,” explains Kearn.
Because of this, an athletic or muscular person could be considered overweight or even obese, when in reality, they are in great shape. If this is the case for you, BMI is a useless metric that you can ignore.
“This would clearly be an inaccurate representation of a perceivably 'poor health condition; and therefore not really matter,” adds Kearn.
Adding to the controversy, your BMI can get in the way of receiving care or qualifying for insurance, Kalmbach says. And it can cause feelings of body shame that just aren’t warranted.
“Only focusing on BMI can be dangerous, as it is just one measure of health. People can become obsessed with their BMI category, leading some to get caught up in quick-fix weight-loss fad diets and not focusing on their overall health,” explains Kalmbach.
And here’s the real kicker: Some people are denied access to care for eating disorders or fertility treatments due to BMI—a metric that was never meant to be used for individual health tracking, let alone for women or people of color.
Many eating disorders, including the most common one, binge eating, do not result in a low BMI. In fact, binge-eating disorder is more than three times as common as anorexia and bulimia combined, and it can cause severe physical and mental health issues when left untreated.
And when it comes to race other than Caucasian, for which it was designed, BMI can be particularly inaccurate.
Accurate Health Indicators to Pay Attention To
A better indicator of overall health is your body fat percentage, according to Kearn and Kalmbach, which includes:
- Waist-to-height ratio
- Body fat ratio
- Stress levels
- Blood pressure
- Cholesterol levels
- Glucose levels (blood sugar)
“Vo2 max and resting metabolic rate are also great indicators of overall health, but they are costly and not readily available,” adds Kearn. Vo2 max can measure your ability to exercise, including how you intake oxygen and your endurance level.
At the bottom of the list? Body weight. “Weight is important, but being an ideal weight doesn’t guarantee health,” says Kalmbach.
When it comes to an overall picture of health, BMI lacks clarity and accuracy. Even if BMI measures were adjusted for race, gender, and age, it would still provide a very narrow idea of what health really is. Remember that what determines wellness is unique for everyone, and there are much better ways of tracking your overall health. The number on the BMI chart, or even the scale, is only a small tool in the toolbox of health metrics. If you are concerned about your weight or other physical or mental well-being factors, speak to your doctor.