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BMI: A Well-Known System But Flawed?

Content warning: This article discusses topics of mental health which could be distressing to some readers.

Measuring tape on top of a scale
By Pixabay

From counting calories to going on the scales, we track our weight. Perhaps at some point in your life, you may have used BMI to measure how much body fat you have. Doctors use this to reduce your likelihood of developing certain weight-related medical conditions like heart disease, stroke, and type 2 diabetes. For a long time, we assumed this was a good system to check you were healthy. But recently BMI has been shown to be unreliable like miscategorising people.

How Does BMI Work?

BMI stands for body mass index. The system was created in the 1830s by Lambert Adolphe Jacques. Your BMI is categorized into 4: underweight, healthy, overweight, and obese. This uses your height and weight to work out if you are in the healthy range, according to the NHS for most adults an ideal BMI is between 18.5 to 24.9. This is done by a calculation: weight in kilograms divided by your height in meters squared.

What Are The Problems?

One problem with the system is that it does not distinguish between muscle and fat. This shows how you could be very muscular and have little body fat, but you would be classified as overweight. Muscle fat is much denser than fat, and Dr David Katz, an expert in preventative medicine said:

"So somebody who's extremely muscular could have a high BMI and yet have a very low percent body fat, which is what you're really concerned with. Somebody who has very little musculature could actually register as lean on the BMI scale, and still have an excess body fat."

So the unreliability of BMI does call into question whether should we still use it. It can also affect people's mental health in particular increasing anxieties over their body image. A recent report from the Women and Equalities Committee warned that the use of BMI can cause a stigma with people's weight and contribute to eating disorders. A report from 2019 found that 31% of teenagers and 35% of adults feel ashamed or depressed because of their body image. With a system that is flawed and can have a negative impact on a person's mental health should we really still use it?

What Else Can We Use?

Since BMI can be unreliable the question is what else should doctors use to measure a person’s health. One way is taking more measurements when calculating a person’s body fat. For example, using abdominal circumference, waist-to-hip ratio, and underwater weighing to look at body density. Instead of using a system to fit everyone perhaps it's time to use a more tailored system based on a person's medical history and take into account their muscle content. So that it can be more reliable and accurate.


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