If you search for “BMI” on Google, the first site that pops up is the U.S. National Institute of Health’s a BMI (body mass index) calculator. The site reads “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. Body mass index is a simple calculation of height and weight; it has nothing to do with body fat. While one can infer that if someone weighs more, they are carrying more body fat, it’s not always the case.
The Canadian Diabetes Association describes BMI a bit better. Their website states “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 the weight is carried as muscle or fat, just the number.”
On a large scale, perhaps BMI can be useful. BMI can show general nationwide trends in body weight and could be useful for statistics. But, BMI loses its usefulness when 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. Here’s why:
1. It’s another number. Even when used within it’s limitations, the BMI is just another number. And despite knowing that it’s just a number, just like the number on the scale (because, essentially, that’s all it is), it’s easy to get caught up with that number. A number can undermine all the positive, healthy changes that you make.
2. It’s 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 clients at Ascend who are extremely fit and very healthy, but are considered overweight according to the BMI scale. They are not body builders; they are strong, fit and healthy individuals. If they lost enough weight to become ‘normal’, then they would become unhealthy. Some people are naturally small; some people naturally have a stronger build and carry more muscle mass. Some people wear a size 8 shoe; some people wear a size 10 shoe.
3. It puts unnecessary labels on people. Even if you’re 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 label ‘normal’ isn’t very effective either. Congratulations. You’re normal.
4. BMI can put unnecessary stress on a healthy individual. Many people already struggle with negative self-image and reading that you’re ‘overweight’ despite being healthy could further promote poor self-image.
5. No one really knows how much you’re supposed to weigh. I know a lot of very fit, healthy people who have a larger body size, or carry a bit of extra body fat. I know some very unhealthy people who are lean.
6. It’s useless. If you legitimately need to lose weight, it’s likely you already know. It’s also likely that an attentive health professional would be able to assess whether their patient really needs to lose weight without the use of a BMI calculator. If this is indeed true, what’s the point of using BMI at all?
7. It can lead to feelings of defeat. Imagine knowing that even if you lose 50 pounds, you’d still be considered ‘obese’. Or knowing that getting to ‘normal’ is an unrealistic goal, even in the best circumstances. If someone legitimately needs to lose weight, any weight loss can positively impact his or her health. Back to point #5: what’s the point of using BMI at all?
BMI is commonly used as a measure of health and predictor of lifestyle related diseases. While it does have some use to measure statistics across a large population, it’s not an effective way to assess health on an 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 health professional. Remember that any healthy lifestyle change, or any weight loss (if you legitimately need to lose weight) can positively impact your health. Disregard what an online calculator says and focus on being healthy.