If you search for “BMI” on Google, the first site that comes up is a BMI (Body Mass Index) calculator from the US National Institutes of Health. The site says “Body Mass Index (BMI) is a measure of body fat based on height and weight that applies to adult men and women”. Except it’s not. 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 bit better. Their website states 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 being carried like muscle or fat, just the number.”

On a large scale, perhaps the BMI could be useful. The BMI can show general national trends in body weight and could be useful for statistics. But, the BMI loses its usefulness in measuring an individual. Even when BMI is used correctly for a person: as a measure of height versus 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 that it’s just a number, like the number on the scale (because, essentially, that’s it), it’s easy to get caught up in that number. One number can undermine all the positive and healthy changes you make.

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

3. Put unnecessary labels on people. Even if you’re aware of the BMI scale’s pitfalls, it can still sting when the online calculator spits out the words “overweight” or “obese.” In fact, the ‘normal’ tag isn’t very effective either. Congratulations. you’re normal

4. BMI can cause unnecessary stress in a healthy person. Many people already struggle with a negative self-image, and reading that they are “overweight” despite being healthy could further promote a poor self-image.

5. No one really knows how much you’re supposed to weigh. I know many healthy, fit people who have a larger frame or have a little extra body fat. I know some very unhealthy people who are skinny.

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

7. It can lead to feelings of defeat. Imagine knowing that even if you lose 50 pounds, you would still be 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 #5: what’s the point of using BMI at all?

The BMI is commonly used as a measure of health and a predictor of lifestyle-related diseases. While it has some use 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 harmful. If you think you could benefit from losing weight; talk to your doctor or healthcare professional. Remember that any healthy lifestyle change or weight loss (if you really need to lose weight) can have a positive impact on your health. Ignore what an online calculator says and focus on being healthy.