Body Mass Index (BMI) is a measure of body fat based on a person’s weight and height. The formula is BMI = kg/m2 where kg is a person’s weight in kilograms and m2 is their height in meters squared.
The Body Mass Index was invented nearly 200 years ago. Its creator, Adolphe Quetelet, was an academic whose studies included astronomy, mathematics, statistics, and sociology. Notably, Quetelet was not a physician, nor did he study medicine. He was best known for his sociological work aimed at identifying the characteristics of l’homme moyen — the average man — whom, to Quetelet, represented a social ideal.
It is often used as a quick and easy way to assess whether someone is at a healthy weight, overweight, or obese. However, there are several reasons why BMI is not an accurate indicator of overall health and well-being:
It doesn’t distinguish between muscle and fat
BMI is a measure of body weight and does not take into account the composition of that weight. This means that a person with a high muscle mass, such as a bodybuilder, may have a high BMI, but still be healthy, while a person with a low muscle mass, may have a lower BMI but be unhealthy.
It doesn’t take into account body shape
BMI does not take into account how body fat is distributed in the body. A person with a “pear-shaped” body, who carries most of their weight in the hips and thighs, may have a lower BMI than a person with an “apple-shaped” body, who carries most of their weight in the abdominal area, even though the latter may have a higher risk for health problems such as diabetes and heart disease.
It doesn’t account for other health factors
BMI does not take into account factors such as overall fitness, muscle mass, and body composition, which are important indicators of overall health and well-being. A person with a high BMI but who is physically active and has a high muscle mass and low body fat may be healthier than someone with a lower BMI who is sedentary and has a high body fat percentage.
A person with a higher BMI does not necessarily indicate poor health, and a person with a lower BMI does not necessarily indicate good health.
What’s a better indicator than BMI
BMI is just a single value that does not differentiate between fat or muscle mass. If you use BMI to track your health progress, you will never know if the changes were in fat or muscle. BMI may also oversimplify health risks. Two people with the same height and weight would have the same BMI and health risks—even if one of them has a healthy amount of fat and high muscle mass.
On the other hand, percent body fat puts your weight into context by showing how much of it is fat mass. Tracking changes in your body fat percentage lets you focus on actual fat loss, not just weight loss, which can also come from muscle mass.
Healthy Range
For BMI, 18.5 –24.99 kg/m2 is the healthy average range according to the World Health Organization.
For percent body fat, the ranges differ for men and women, as women tend to carry more body fat than men due to their reproductive system and genetics. For men, the healthy range is between 10-20%. For women, the healthy range is between 18-28%.
