The Body Mass Index

It’s a fact that comes up again and again in studies: many overweight people don’t believe they’re overweight, while many people who are at a healthy weight, mistakenly think they’re too heavy. But how do you know the appropriate weight for your height and age? 

Comparing yourself to the people around you is no use - you may live with other overweight people and therefore think your body is just fine, or perhaps you’re constantly surrounded by models and have a distorted view of what “thin enough” means. Since the levels of overweight vary by country, someone looking at the people around them in the United States would see a very different body ideal than someone living in the Netherlands. 

The truth is, an accurate measure of whether or not you’re at an appropriate weight would incorporate your height, age, muscle-fat ration, sex and bone density. But that would require expensive scans and testing, so for now, the best tool we have is the Body Mass Index (BMI).

What is your BMI?

In metric units, it’s your weight in kilograms divided by the square of your height in meters. In imperial units, it’s your pounds times 703, divided by the square of your height in inches. If your BMI is less than 18.5, your underweight. A BMI between 18.5 and 25 is ideal, between 25 and 30 is overweight, and an individual with a BMI over 30 is considered obese. 

Still, there are problems with the BMI. It doesn’t take into account the difference between fat and muscle, so a toned sprinter may have the same BMI as a dedicated couch potato. Many athletes have BMIs that erroneously push them either into the “overweight” or even “obese” range, when they’re simply muscular (and remember, muscle weighs more than fat.)

The BMI also doesn’t account for bone density. An individual with osteoporosis (low bone density) may have much more body fat than an individual with healthy bones, yet still have the same BMI. There’s another flaw with BMI: it tends to tell short people that they’re thinner than they really are, and tall people that they’re heavier. Some scientists have suggested a different way of calculating BMI to make up for this problem.

Many people say the BMI is of no use for individuals, and should only be used for population-wide measures (for example, to see if Americans in general are getting heavier.) Others say it’s useful as a ballpark measure. Still others say other measurements - for example, your waist-to-hip ratio - are best for determining if you’re over or underweight.

If your weight is a concern for you, speak to your doctor or chiropractor. He or she will be able to tell you if your body weight is healthy or unhealthy and suggest lifestyle changes if you’re too heavy. 

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