Don’t Trust Your BMI

It’s a widely used measure of health and fitness. And it’s often wrong. I’m talking about BMI – Body Mass Index.

Doctors will often look at it and decide whether you need to go on a diet or not.

Your insurance company may use it to decide to raise your rates.

You can find BMI calculators online. Don’t go searching! Here’s one for you to use.

Here’s their definition of BMI:

BMI (Body Mass Index) is a measurement of body fat based on height and weight that applies to both men and women between the ages of 18 and 65 years.

BMI can be used to indicate if you are overweight, obese, underweight or normal. A healthy BMI score is between 20 and 25. A score below 20 indicates that you may be underweight; a value above 25 indicates that you may be overweight.

Notice their careful use of language: “a value above 25 indicates that you MAY be overweight.”

Then again, you may be completely fit and healthy!

Muscle Mass

bmi fail? woman with arm muscles

Woman with arm muscles

Take a look at this article by Oscar Schneegans on his blog The Snowgoose Chronicle.

Oscar quotes from a research study that shows your muscle mass is a better indicator of health and longevity than your BMI.

I’m on record stating that BMI is a crock. I arrived at that conclusion through reasoning, not scientific research. But now there is scientific research that demonstrates that BMI is a poor predictor of longevity, and that muscle mass is a better predictor of longevity.

Here’s from the abstract of the study he quotes:

Obesity (as defined by body mass index) has not been associated consistently with higher mortality in older adults. However, total body mass includes fat and muscle, which have different metabolic effects. This study was designed to test the hypothesis that greater muscle mass in older adults is associated with lower all-cause mortality.

In fact, the researchers did find that older adults with greater muscle mass survived longer than those with less muscle.

Common Sense

woman lifting weights

It seems to me that the results of this study should just be common sense.

BMI treats a pound of muscle the same as a pound of fat. We all know that it’s better to have muscle rather than fat. But, BMI cannot distinguish between the two.

Hence, you hear lots of stories of healthy adults who workout and have lots of muscle mass being told that their BMI is too high.

It’s time to measure muscle mass as well as BMI.

Picture Credit: Flickr – imagesbywestfall
Shlomo Skinner
 

I'm the one who writes most of the posts here at Fitnessator. I'm a former US Marine trying to stay in shape. I enjoy using different fitness equipment as well as body weight exercises and eating lots of healthy greens.

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