Body mass index, or BMI for short, is a measure of your body fat based on your weight and height. In general, the higher the BMI, the more at risk a person is of being considered overweight or obese. In fact, BMI is the number one indicator used to measure obesity around the world. But BMI has faced a lot of backlash [1] in the past for not being an accurate representation of a person's health or fitness level.
BMI is simple to understand, and you can see how to calculate yours here [2]. You take your weight in kilograms and divide it by your height in meters squared. Based on the number you get, you can fall into any of the four categories below for both men and women:
- Underweight: BMI is less than 18.5
- Normal weight: BMI is 18.5 to 24.9
- Overweight: BMI is 25 to 29.9
- Obese: BMI is 30 or more
BMI just tells you that the number on the scale matches what is expected of your height. Nothing else is taken into consideration like age, sex, muscle mass, or body fat percentage. A pound of fat takes up a lot more space in your body than a pound of muscle, so it's important to not rely on the scale or BMI too much. If you are on a new fitness or health journey, I encourage you to take progress pictures and use the reflection of your body in the mirror to showcase the changes happening.
Also, where your body stores its fat is another key factor that BMI cannot tell you. Some people pack fat in central areas of their body like the chest and stomach, which is more risky compared to fat packed in the thighs or arms. BMI can be misleading for both thin-looking and thick-looking people.
Although BMI has its cons, it still does a pretty good job of predicting if someone is at risk of disease. Especially for children who have not developed much muscle mass yet in comparison to adults, BMI is a very useful tool.
If you're on a weight-loss journey or weight-gain journey or you simply want to assess your health, there are scales that measure your BMI [5] along with your bone density, muscle mass, and body fat percentage. Your mental attitude toward your body is just as important as its physical state. This is why it is so important to take your BMI with a grain of salt. A person who falls into the underweight or normal weight category can still be considered skinny fat, and a person who falls into the overweight category may actually look very lean and slim but just has more muscle. Sometimes when people are trying to lose weight in extreme ways, they see the number on the scale go down and get excited. In reality, though, your body might just be in survival mode where it's going to break down muscle to get energy all while holding onto fat tighter. On the other hand, if you see your BMI or weight go up but body fat percentage go down, celebrate because you're on the right track. Don't forget muscle weighs more than fat. Strong is beautiful!