Do You Know Your Body Mass Index (BMI)? Here’s All The Reasons You Absolutely Should


BMI, or Body Mass Index, has been used for years as a good guide for body composition and helping to identify underweight, healthy weight, or overweight because it takes into account your frame size. It provides an important part of the picture, but it has some limitations as well.

The positives:

The BMI provides a measure that is more robust and meaningful than simply weight or a waist circumference, though each of those also offer important information. The number on a scale does not take into account your height or your fat and lean mass. Waist circumference gives one measure on a body with many measures, so also only tells a partial story. Body mass, however, does take into account height in addition to weight which adds more information, but it still doesn’t ‘see’ body fat/lean weight directly. Research has shown that our Body Mass Index correlates well as an indicator of one’s weight in the underweight, healthy, overweight or obese categories with a large part of the population.

Even though it’s not today considered the gold standard assessment tool that it was at one time, many doctors, health care professionals and personal trainers still use this measurement as a powerful indicator that offers quick and handy information about weight based on frame size, as well as potential health risk factors.

The limitations:

There are some limitations to this measurement. The downside is that this measurement tool may overestimate body fat if you’re an athlete or if you’re very muscular. It can also underestimate body fat if you’re older and have lost muscle mass. It is important to remember that although BMI correlates with the amount of body fat, it doesn’t directly measure body fat. Just because there are limitations doesn’t mean that it’s meaningless. Consider knowing your BMI as one piece of your health picture. Each tool adds dimension to your health story and it’s also very helpful for setting goals.

How to use your Body Mass Index:

It’s all about context. Just like a bad hair day does not define your whole look or your every day thankfully, a BMI number is not the sum total of your health picture either. It is one of a few different measures that can help build an overall picture of your health, weight, fitness and body composition. And it can help you set goals by providing a baseline. However, don’t rely on this as your only weight assessment tool. I actually believe the measuring tape, the scale, the way our clothes fit, and the mirror (how you look and feel when you smile into the looking glass) are among the most helpful tools to help monitor health as it relates to our body composition. But BMI is important to know as a piece of the big picture. You can establish goals that include your own number within the BMI ranges as they relate to your personal health.

Are You at a Healthy BMI?

These are ranges of BMI’s for healthy and other weights categories. What they do show is that health risk increases if the Body Mass Index moves into the overweight and obesity categories. But even within the healthy range, weight gains can carry health risks for some adults. Alternately, having a low or high BMI may not necessarily indicate a significant health risk. However, the BMI is one important number to pay attention to when looking at your whole health picture.

Underweight: BMI less than 18.5 is considered underweight.
Healthy Weight: BMI from 18.5 up to 25 refers to healthy weight.
Overweight: BMI from 25 up to 30 refers to overweight.
Obese: BMI 30 or higher refers to obesity. Obese persons are also considered overweight.

What Is My BMI?

BMIThe equation for BMI starts with knowing your weight in kilograms and dividing your weight by your height in meters, squared. Got that? Well if you’re a math whiz, you might, but thankfully there are easier ways to get there. The long form equation requires converting your weight from pounds to kilograms (divide by 2.2) and then converting your height in inches into meters (multiply by 0.0254) and then squaring this number. Finally, divide the height-squared into the weight and you have your BMI.

There are a number of apps and online calculators you can find by searching “BMI calculator” and enter your weight and height. Knowledge is power, and it’s how we take control of our health and lives.

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