What Is My BMI and Does It Matter?

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What is a healthy BMI?

What is your BMI? You might not know off the top of your head, but at some point in time you probably knew your body mass index.

You can easily determine your own BMI with an online calculator or by doing the math longhand. But what really is BMI, and how much does it matter? Farm to Fit found out!

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What is BMI and where did it come from?

BMI stands for Body-Mass Index, and is a calculation derived from your body weight and your height. For decades, the measurement has been used in medical studies and physician’s offices alike. The original equation was developed in the 1830s by Jaques Adolphe Quetelet, a Belgian mathematician, statistician, and astrologer. Notably, he had no medical credentials. 

By dividing body weight by height squared, Quetelet believed he could estimate and categorize human body types into healthy weight, underweight, overweight, and obese. Contrary to its modern usage, he created BMI as a statistical value rather than a measurement of individual health.

BMI as we know it now developed in the US during the early 1970s, when a researcher named Ancel Keys needed a simple measurement for body weight in relation to height. By the 1990s, the National Institute of Health had started using BMI to categorize obesity in all races, ages, sexes, and cultures in the US.

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What’s a healthy BMI? What’s a normal one?

A healthy BMI is considered to be between 18.5 and 25 kg/m2 . Those with BMIs under 18.5 kg/m2 are considered underweight. People with BMIs over 25 kg/m2 are considered overweight and those with values over 30 kg/m2 are considered obese. 

The normal BMI, aka the mean, has been slowly shifting towards 25 kg/m2 in the US since the 1970s. Adult BMI over 30 kg/m2 is much more common.

While a “normal” or “healthy” BMI might be an encouraging sign, this simple measurement can’t tell you if you’re healthy or not. Many people live full, healthy lives with high BMIs, and many people with low or average BMIs are unwell. 

In some ways this makes sense, we wouldn’t tie our entire bodily health to our blood pressure or heart rate. But then why is the BMI, an outdated and arbitrary measure, still used so centrally in individual health care? Does it actually matter?

Does my BMI matter?

Put simply: Not much. BMI is still used as widely as it is because it’s such a simple value to calculate, not because it’s accurate or especially useful. Many healthcare providers still use BMI as an initial estimate of a patient’s overall body fat, though not as a diagnostic tool. 

There’s strong evidence that as BMI increases, there’s a correlated rise in health risks for type 2 diabetes, high blood pressure, and heart issues. While this is useful knowledge, it’s important to note that these risks are caused by excess fat. BMI cannot distinguish between the weight of muscle and the weight of fat, meaning muscular people are often classified as obese, despite having little fat. BMI is also unable to distinguish where fat is stored on your body, which can be a factor in how detrimental excess fat is to your organ health. 

Another major flaw in BMI’s measurement chart comes from its sample groups. As previously mentioned, the original equation was created by a Belgian researcher, who only examined and recorded European white men’s bodies when formulating his index.

As such, the BMI measurements of women and people of color are often inaccurate, labeling many as obese or overweight when they are in truth within healthy variances. Classifications like “obese” and “overweight” may further deter members of these communities from seeking care due to the stigma.

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BMI is still in use by many physicians and researchers as a cheap, easy measurement of body fat.

While it has many drawbacks, it’s useful as an initial indicator of potential weight related risk. New measurements like waist-to-height ratios or waist circumference may make for a more accurate measure, and other more invasive methods of fat measurement are becoming more available. Until then, your doctor may still end up using that BMI calculator.