How concerned should you be about your BMI?

I consider myself a healthy person. I eat lots of fruits and vegetables, love fiber, eat rocket twice a week and try to sneak it in for lunch on the days I don’t have it. But when I recently calculated my body mass index (BMI), which involves dividing a person’s weight by the square of their height, I was in for a surprise: I’m overweight.

For many of us, such news may sound alarm bells. Especially for someone like me who has a history – in my early teenage years – of being unhealthily preoccupied with where the dial is placed on the weight scales. But how concerned should we be about our BMI, really?

For starters, you should understand that this scale was never intended to evaluate an individual’s health. It wasn’t even created by a doctor or anyone with any medical training, but rather a 19th century mathematician named Adolphe Quetelet who wanted to track the height and weight of the entire population. No offense to the numbers gurus, but this isn’t exactly a promising origin story for Health Metrics.

If we fast forward to the 1970s, this measure started gaining popularity as a quick and cheap way to measure body fat levels and obesity rates: all it took was a tape measure and some weighing scales. Then, in 1997, the World Health Organization—because of BMI’s simplicity—recommended it as a health assessment tool.

In the following years, measurement became deeply embedded in healthcare systems. It now has access to dozens of treatments, from knee surgery to GLP1 weight-loss drugs and fertility treatments. In general, if a person’s BMI is below 18.5, they are classified as underweight; If it is between 25 and 29.9, they are overweight, while a number above 30 indicates obesity. The rationale is that limiting treatment to specific BMI brackets can reduce safety risks and increase success rates.

But there is a big problem. BMI does not differentiate between bone, muscle and fat. This means that someone who is very muscular with little body fat may fall into the overweight – or even obese – category, despite being physically fit and strong.

I, for one, had a “healthy” BMI, but (to my delight) rock climbing gave me real, noticeable arm muscles for the first time in my life – and I suspect that’s partly what pushed me into the overweight group.

In other cases, people with a “healthy” BMI may lack body fat to the point where they stop menstruating, which can lead to problems like fragile bones, heart attack and infertility. Obviously, this is not correct.

And that’s not all. BMI does not account for where fat is stored in the body. But we know that the fat around our abdominal organs, known as visceral fat, increases the risk of many conditions – such as heart disease, high blood pressure and type 2 diabetes – found in the arms, lower back and thighs.

I am not saying that BMI is completely useless. In some cases, this is actually a sign that a person would benefit from medical care to help gain or lose body fat.

But we now have other, much better ways to measure body fat levels. For example, one important study found that the waist-to-hip ratio, which involves dividing the waist circumference by the hips, beats BMI when predicting a person’s risk of heart attack. Another showed that it was a good predictor of mortality.

There is also a weight-adjusted waist index, where you divide your body weight by the square root of your waist circumference. Similar to waist-to-hip ratio, it puts more emphasis on harmful visceral fat and has been shown to improve BMI.

Another alternative is the Body Circumference Index (BRI), which uses height, waist circumference and weight data to measure body shape. Studies have shown that the BRI predicts total and visceral fat levels better than BMI, waist or hip measures alone. We also have devices that zap the body with low voltage electricity, indicating where the fat is spreading around the body.

So, if you are concerned about your weight, these alternatives are more informative than calculating your BMI. But personally, I think that instead of worrying too much about specific numbers, most of us are better off focusing on healthy lifestyle habits like eating lots of fruits and vegetables, maintaining social connections, getting enough sleep and engaging in regular exercise. That’s definitely what I do!