Is Your BMI Misleading You?

If you’ve ever had your weight measured (either at a hospital or using those electronic measuring machines in the street), then you’ve probably had your BMI calculated.

Body Mass Index (BMI) is a simple formula that’s used to estimate whether someone’s weight is within a certain range for their height.

It’s calculated as:

BMI = weight (kg) ÷ height (m)²

After calculating your BMI, you fall into one of these categories:

• Underweight: BMI below 18.5

• Normal weight: BMI 18.5–24.9

• Overweight: BMI 25–29.9

• Obese: BMI 30 or higher

BMI was first called the Quetelet Index after Belgian mathematician Adolphe Quetelet, who developed it in the 1830s.

It wasn’t until the 1990s that big health organizations like the World Health Organization (WHO) adopted BMI as a quick and convenient way to categorize body weight.

Today, it’s still used widely in medical settings, despite its major flaws.

Why BMI is flawed

When it was established from multiple studies that excess weight (specifically body fat) increases the risk of conditions like heart disease and diabetes, there was a need for a quick and simple tool to screen for obesity-related health risks.

BMI fit the criteria perfectly: it’s cheap, easy to calculate and doesn’t require any special tools or tests.

However, it poses a huge problem.

BMI measures total body weight. This is the accumulative weight of your muscle, organs, water content, bones, and fat.

It doesn’t directly measure body fat.

And since body fat (not weight) is what’s been linked to an increased risk of disease, then BMI actually tells you nothing about how healthy or unhealthy you are.

BMI assumes all weight is the same. But muscle and fat are completely different.

Unlike fat, having more muscle has been linked to better metabolism, improved insulin sensitivity, and lower disease risk.

But because muscle is heavier than fat, using BMI alone can misclassify people in significant ways.

This flaw is even more pronounced in specific groups of people like:

• Muscular individuals - Someone with a high muscle mass may be classified as being “overweight” or “obese” even if they have very little body fat and excellent health.

• Older people - As people age, they naturally start to lose muscle mass and accumulate more fat. An elderly person with a “normal” BMI may still have high body fat and be at higher risk for health problems.

Additionally, BMI doesn’t take into account where you store fat.

Typically, you store fat in 2 main sites:

• Subcutaneous fat - The fat just under your skin, which is generally less harmful.

• Visceral fat - The fat stored around your organs (especially in the belly), which has been linked to increased risk of diabetes and heart disease.

Because BMI doesn’t consider this, a person with smaller arms and legs but a large belly could have a “normal” BMI yet be at a high risk of metabolic diseases due to excess visceral fat.

Despite how commonly it’s used, BMI completely ignores some of the most important factors that determine health.

What to use instead

Because of these shortcomings, one method that estimates visceral fat more directly has been suggested as a better alternative to BMI:

The waist-to-height ratio.

To calculate it, you measure your waist circumference (around your belly button) and divide it by your height in the same units (waist circumference ÷ height).

Your waist should be less than half of your height (a waist-to-height ratio that’s equal to or less than 0.5).

For instance, if you’re 170 cm tall, your waist should ideally be less than 85 cm.

Why is this better?

Waist size is a strong indicator of visceral fat, which is directly linked to a higher risk of disease.

One study found that individuals with a “normal” BMI but high visceral fat (indicated by a waist-to-height ratio above 0.5) have the same, and possibly higher, health risk compared with those classified as overweight or obese by BMI.

In other words, how much belly fat you have matters more for health than just your weight.

But while waist-to-height ratio is a better predictor of metabolic health than BMI, it’s still just one piece of the puzzle.

Other indicators like your blood pressure, cholesterol level, blood sugar level, and physical activity level provide a more complete picture of your overall health.

Thanks for reading! I hope you found something valuable :)

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