If you Google “BMI”, the first site that appears is the US National Institute of Health’s BMI (Body Mass Index) calculator. The site says “Body Mass Index (BMI) is a measure of body fat based on height and weight as applied to adult men and women. ” Except it isn’t. The body mass index is a simple calculation of height and weight; it has nothing to do with body fat. While it can be inferred that if someone weighs more, they have more body fat, this is not always the case.

The Canadian Diabetes Association describes BMI a little better. Their website says that “BMI is not used for muscle builders, long distance athletes, pregnant women, the elderly, or young children. This is because BMI does not take into account whether weight is carried as muscle or fat, just the number “.

On a large scale, perhaps BMI can be helpful. BMI can show general national trends in body weight and could be useful for statistics. But, the BMI loses its usefulness when measuring an individual. Even when BMI is used correctly for a person – as a measure of height vs. body weight, I still don’t like it. This is why:

1. It’s another number. Even when used within its limitations, BMI is just another number. And despite knowing it’s just a number, just like the number on the scale (because, essentially, that’s it), it’s easy to catch up on that number. A number can undermine all the positive and healthy changes you make.

2. It is inaccurate for more people than just extreme athletes or muscle builders. BMI does not take into account bone density or muscle mass. I can easily name many Ascend clients who are extremely fit and very healthy, but are considered overweight on the BMI scale. They are not bodybuilders; they are strong, fit and healthy individuals. If they lost enough weight to become ‘normal’ then they would become unhealthy. Some people are small by nature; some people naturally have a stronger constitution and have more muscle mass. Some people wear a size 8 shoe; some people wear a size 10 shoe.

3. Labels people unnecessarily. Even if you are aware of the pitfalls of the BMI scale, it can still hurt when the online calculator spits out the words “overweight” or “obese.” In fact, the “normal” label is not very effective either. Congratulations. You’re normal

4. BMI can put unnecessary stress on a healthy person. Many people already struggle with a negative self image and reading that you are “overweight” despite being healthy could further promote a poor self image.

5. No one really knows how much you are supposed to weigh. I know many healthy and very fit people who have a larger body size or have a little extra body fat. I know some very unhealthy people who are thin.

6. It is useless. If you legitimately need to lose weight, you probably already know. It is also likely that an attentive healthcare professional can assess whether your patient really needs to lose weight without the use of a BMI calculator. If this is true, what is the use of using the BMI?

7. It can provoke feelings of defeat. Imagine knowing that even if you lose 50 pounds, you are still considered “obese.” Or knowing that getting to “normal” is an unrealistic goal, even under the best of circumstances. If someone legitimately needs to lose weight, any weight loss can have a positive impact on their health. Going back to point n. 5: what’s the point of using BMI?

BMI is commonly used as a measure of health and a predictor of lifestyle-related illnesses. While it has some utility for measuring statistics in a large population, it is not an effective way to assess health at the individual level. In fact, the repercussions of using BMI could even be detrimental. If you think you could benefit from weight loss; talk to your doctor or healthcare professional. Remember that any healthy lifestyle change or weight loss (if you legitimately need to lose weight) can have a positive impact on your health. Ignore what an online calculator says and focus on being healthy.