Did You Know #12: All About That BMI

Happy Friday, friends! Are you ready to get nerdy about nutrition with Did You Know? I realize it’s not the first Friday of the month (when we usually do these link-up posts)..but better late than never, right? Honestly, all 3 of us kind of forgot about it last week due to the holidays. I send a text last Friday like, “uh..oops.” It made me feel a liiittle better that I wasn’t the only one that forgot.

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My topic for today isn’t necessarily new, but it’s something that I’ve been thinking about lately. 

BMI. Or Body Mass Index.
This is a tool that is used to assess body fat using height and weight ratios. Let’s get nerdy and chat about it!

BMI. Or Body Mass Index.

This is very topical as it’s the beginning of the year and many are aiming to better their bodies. This generally means losing weight to either look better or to get healthier.

But what is healthier? 

The answer is never simple since there are many factors that need to be taken into account.

One factor is body fat. There is a general consensus with health care professionals that if your body fat is within a certain range, you are at a lower risk of chronic disease.

There are several ways to figure out your body fat, but one of the easiest that is used by most doctors, personal trainers and dietitians is the BMI or Body Mass Index. This tool simply uses height and weight plugged into a handy formula that will give you an estimated body fat.

Using the metric system: weight (kg) / [height (m)]².

For us Americans, there is a conversion factor: weight (lb) / [height (in)]² x 703

Here’s an easy calculator.

The number you receive is then evaluated:

Underweight: under 18.5

Normal: 18.5-24.9

Overweight: 25-29.9

Obese: 30 and over

 

[ image source ]

 

How did these numbers come about?

In the 19th century, a gentleman named Adolphe Quetelet came up with a system to measure excess fat using weight adjusted for height. Ancel Keys reworked it in the 1950s and called it the BMI which is the same system we use today. (2.) The “normal” range was adjusted in 1998 from 18.5 to 27.8 to what we use now which is 18.5 to 25.

 

Benefits of using the BMI:

-It works for the majority of adults to assess health risks.

-It’s easy to use; no invasive tools or expensive equipment is required.

 

Issues of using the BMI:

The BMI isn’t always accurate at assessing body fat because it doesn’t consider bone or muscle mass (ex. not everyone has the same proportion of bone or muscle mass). This means that the BMI tool:

-Underestimates body fat for older adults and those with low muscle mass.

-Overestimates body fat for those who are very muscular.

-Isn’t able to assess the health risks of those with excess abdominal fat (those with excess abdominal fat are at higher risk than those who carry their fat lower like in the hip and thigh region). (3.)

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Other notes:

-Physical activity plays a major role in using the BMI assessment. Even if you fall into the overweight range, you can almost eliminate your risk for chronic disease with regular exercise. (1.)

-Some recent studies argue that the normal BMI range should be at higher range, especially for middle aged adults. (1.)

-If you are assessing your own BMI, try to use a chart or a site that takes age and sex into consideration.

 

Personal Note:

Some gyms categorize numbers lower than 18.5 as “athletic,” but this does not change the fact that those with a lower than 18.5 body mass have a higher risk of chronic disease.

I have had the experience before, sitting with a personal trainer at a new-to-me gym, where I was at a 20% body fat level and somehow arrived at the conclusion that I needed to lower my body fat. Looking back, that seems crazy, but seeing the chart somehow made me feel like I needed to get leaner.

I basically want to warn you guys: don’t fall for it. It is especially important for women to maintain a healthy level of fat for proper hormone levels and protection against disease. Body fat is essential for us to function; too little is just as unhealthy as too much.

[Tweet “Let’s get nerdy and real about BMI. #diduknowlink #realtalk”]

Sources:

1. http://jama.jamanetwork.com/article.aspx?articleid=1555137

2. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2065990/

3. http://www.mayoclinic.org/bmi-calculator/itt-20084938

 

Now it’s your turn! Link up your fitness, nutrition or health-related posts here!

Eat and move happy! Tell me….

What are your thoughts on using the BMI?

Have you ever felt uncomfortable in a personal training assessment?

 

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