Is Body Mass Index (BMI) a Good Way to Evaluate Obesity?

What is the Body Mass Index (BMI)?

BMI is a number calculated from a person's weight and height. It is sometimes used to diagnose obesity in adults, but it can be misleading. Tests, screens and assessments have a tendency to remain in popular usage even when proven they can be flawed for the reason that there isn’t another option available. I believe that is the reason why the body mass index (BMI) is still commonly used today to determine if someone is obese or not. Doctors will tend to use this as opposed to body-fat percentage. I believe the BMI is flawed and I wanted to share my opinion on why I feel this way.

The Problem with Body Mass Index (BMI)

Is BMI Accurate?

My beef with BMI goes back almost twenty-five years. I was twenty-seven and was about to get engaged. My soon to be fiancé, who is now my wife, and I were living together, and I felt the responsible thing to do at that time was to get a life insurance policy. I felt due to my youthful age and good health, I could lock in a low rate that would carry me for years to come. I should also disclose that at the time I had just competed in Mr. Junior USA Bodybuilding Championships as a light-heavyweight. I weighed 235 pounds with a bodyfat level approximately 12 percent. When I applied for the policy, I was initially denied coverage due to excessive obesity. I eventually was granted a policy after I took a photo of myself in my underwear providing visual proof for underwriting that I was not obese. Why did this happen?

How to Calculate Body Mass Index (BMI)

BMI is not a scale of body-fat or body-composition, but simply a calculation of total mass. If you are short and carry more than the average in lean muscle mass, you will have a higher reading. The way you calculate BMI is as follows:

The formula for calculating BMI is (weight in pounds x 703) / (height in inches)².

To calculate BMI:

     1.    Multiply weight in pounds by 703.

     2.    Multiply height in inches by itself.

     3.    Divide your answer from Step 1 by your answer from Step 2 to calculate BMI.

To interpret the final number:

• A BMI below 18.5 means that a person is underweight.   

• A BMI between 18.5 and 24.9 is “normal.”

• A BMI between 25 and 29.9 indicates that a person has overweight.

• A BMI above 30 indicates that a person has obesity.

My BMI when I was 27 years of age was 35. At 52 years of age, I’m currently 198 pounds with a slightly higher body fat level and my current BMI is 29.

The BMI has limitations because it doesn’t take in consideration lean muscle, bone mass, and body-fat percentage. The factors are relevant to assessing someone’s overall health. Another issue I have with the BMI is that it doesn’t take into consideration where fat is in the body. This is relevant to someone’s overall health. It’s been proven that excessive fat around the abdomen is a high-risk factor for both diabetes and cardiovascular disease. 

The challenge is that there are not currently any standards for body-fat levels. There are recommendations, but these are subjective.[1] Below is a good benchmark for determining where you stand in regard to body-fat levels. 

Body fat percentage table for men

Mens BMI Age 20–29

Mens BMI Age 30–39

Mens BMI Age 40–49

Mens BMI Age 50–59

Mens BMI Over 60

Body fat percentage table for women 

Women usually have slightly more body fat than men due to an increase in essential fat. Body fat also changes with age.

Womens BMI Age 20–29

Womens BMI Age 30–39

Womens BMI Age 40–49

Womens BMI Age 50–59

Womens BMI Over 60

Now I will admit that calculating body fat does come with its issues. It does require more than math. You need equipment. There’s underwater weighing, x-rays (DEXA), air displacement plethysmography, and my personal favorite skinfold calipers. There is an element of human error when using the calipers, but it is minimal. It is recommended that you use the same technician to minimize the risk of error. So next time you visit your doctor for your annual physical and she tells you that your BMI is high, don’t panic, it may not be that bad. 

I’ll see you at the J&D Fitness studio!

Source: 

[1] Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index | The American Journal of Clinical Nutrition | Oxford Academic (oup.com)