BMI : Is the Number Significant?

"What should I weigh? " is one of the most commonly asked questions I see in the fitness field.

There are many commonly used measurements to determine a person's general health status. The average American, and even fitness and health professionals tend to focus their energy on their scale weight. Even now, most health professionals (i.e. some doctors) use BMI (Body Mass Index) in assessment of a person's health risks. Thankfully, because of the following information I am about to give you, the number determined by BMI calculations no longer hold the significance they once did.

Let me explain. 

What is BMI? 

Body Mass Index is a height to weight ratio that was implemented by the National Institutes of Health (NIH) in June 1998 in an effort to get health professionals on the same page for assessing health related risks; specifically obesity.

How Accurate is BMI as a Health Measuring Tool?

It seems that BMI accuracy is difficult to calculate, but is a reasonable measurement for assessing obesity rates in comparison with under to healthy weight individuals. A BMI of > 25 means overweight, a BMI > 30 indicates obesity and <25 indicates underweight. 

The problem with BMI is that it does not take in to account factors other than height, weight and gender such as: body fat percentage, muscle mass, lean mass, bone density and structure. This can especially become a problem with dealing with athletes, bodybuilders, men (generally speaking for the athletic male), and the elderly. 

Another noted problem I have found in my research is that BMI was developed based on Caucasian men and women. It is no secret that different races have different body compositions. Consider the following finding from a 2009 study performed on BMI accuracy at Baylor College of Medicine and the University of Houston in a study published in the British Journal of Nutrition in comparing BMI conclusions to DEXA scan conclusions:

"It's important to break down the BMI numbers," Bray said. "Just because you weigh a certain amount doesn't necessarily mean you are overweight. Take, for example, an athlete who is very muscular and still weighs up to 300 pounds."

When the two results were compared, researchers found that the DXA estimate of percent fat of African American women was 1.76 percent lower for the same BMI compared to non-Hispanic white women. Since BMI is assumed to represent body fatness, an African American woman would not be considered overweight or obese until she reached a higher number than what is indicated by the current BMI standards. The opposite is the case for Hispanic, Asian and Asian-Indian woman. Their percent fat is higher by 1.65 percent, 2.65 percent and 5.98 percent, respectively. So they would be considered overweight or obese at amounts lower than what the BMI standards indicates. The results for men were similar.

This is only one example of many studies conducted on the accuracy of BMI, but most findings conclude that BMI is not the most accurate measurement of obesity or general health. 

What are Some More Accurate Measures of a Healthy Body Composition that you Should Consider ?

• Skinfold measurements
• Underwater weighing
• Bioelectrical impedence
• DEXA - Dual Energy X-Ray Analyzer
• Bod Pod (Air Displacement)

How Accurate are these Methods? 

(Listed High to Low)

1. DEXA Scan- New technology found to be the most effective tool for measuring. 
2. Underwater Weighing - Approximately +/ - 1.5% marginal error
3. Skinfold Measurements - Approximately +/- 3% error (if conducted properly)
4. Bioelectrical Impedence -  Approximately +/- 3% error 
5. Bod Pod -  Approximately +/- 3% error 

Please keep in mind that each of these measurements have cons including (not limited to) : cost and availability of equipment, trained professional usage (are they skilled and accurate every time they measure?), getting wet, difficult variables to control (such as hydration and eating prior to testings).

If you are considering evaluating your body composition in comparison to your health status and / or risk factors, contact a trained professional to have one of these tests conducted. If you'd like to learn more about each of these tests individually I have included a link on this blog to New Fitness that breaks down each measurement in a very easy-to-read way. Click here: Body Composition Measurement Testings

REMEMBER: The mirror is your friend. Make it your friend if it's not already. Stop focusing on numbers, and start focusing on being healthy! You only have one body. Make it work for you!