Pear, apple, hourglass, triangle or oval. As humans, we come in lots of shapes (fruits!) and sizes. And often, it can reveal quite a bit about our health—but it’s only one piece of the puzzle.
Doctors don’t rely on body shape alone to know how healthy you are. They use a few tools, one of which is called body mass index (BMI).
What is body mass index (BMI)?
“BMI is a calculation that uses a person’s height and weight to produce a number that assesses their weight category and whether they are at greater risk for disease, such as heart problems and diabetes,” said Samuel Saltz, DO, a bariatric surgeon at Banner Health Center in Fort Collins, CO. “This value provides a simplistic number to estimate a person’s weight as it applies to generally accepted normal targets.”
Based on your BMI index, you will fall somewhere on a scale, which classifies your weight into four categories: underweight, normal, overweight or obese. Although not a perfect tool (we’ll discuss why in a minute), BMI is an inexpensive tool and an easy screening method.
How can I calculate my BMI?
If you have a pen and paper, you simply divide your weight by the square of your height (Kg/M2). Or you can calculate your BMI here on the Centers for Disease Control and Prevention (CDC) website.
What can your BMI be helpful for?
“BMI is helpful to know in the context of seeking treatment for obesity because it allows for classification and risk profiling, which can be used to support choosing a treatment option that can reduce these health risks,” Dr. Saltz said.
Why could your BMI be inaccurate or misleading?
As with many screening tools, BMI does have some limitations. Since people around the world have different body structures and compositions, the value can be misleading if misapplied.
Some experts argue that it’s not an accurate method since many athletes and others with lean muscle mass (like bodybuilders) may fall higher on the BMI range, giving the appearance they are overweight or obese.
In addition, different parts of the world adjust the classification to reflect these differences. For instance, the National Institute of Health determined that a BMI of 25 to 30 is considered overweight. However, in some Asian countries, overweight is the classification for persons with a BMI of 23 and above.
“It is important to understand that BMI allows us to classify persons into risk categories for health and disease and even death,” Dr. Saltz said. “These classifications are based on population studies using a large number of subjects. It can be helpful at the individual level but should not be considered as the only measure of health.”
Other key numbers are important in determining health and risk including your body composition (% body fat) and your body fat distribution.
So why does your BMI still matter?
There are other methods to measuring your body composition, often with measuring devices and waist measurements and ratios, but BMI is easy and affordable making it a desirable tool for many large organizations and health care professionals.
“The best measures are obtained with an inexpensive process that is noninvasive, easy to obtain, reproducible, accurate and applicable across a broad spectrum of the population,” Dr. Saltz said. “In that sense, BMI is really quite good and that is why it is used in medical practices and is a value that insurance plans refer to for the purpose of approving treatment plans.”
While BMI isn’t a perfect measure of body fat percentage, it can play a valuable role in determining your current health and fitness level.