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What’s Wrong with BMI?

By Anne Keckler | March 21, 2008

We’ve all heard that we have an obesity epidemic in the United States. It’s true that more and more children, as well as adults, are overweight. But obesity is being defined by BMI, or Body Mass Index. Is this a good indicator of obesity?

I don’t watch TV at home (but I make up for that by spending all my time on the computer), but while I was away I happened to catch a few minutes of some morning news show. The guests were talking about whether it’s possible to be fat and healthy. Rachel, author of The F-Word blog told her story of losing weight, and losing her health along with it. She was trying to attain an “average” BMI, and she ate an 800-calorie diet while exercising for two hours each day just to maintain that BMI once she reached it. Her journey took her from being 300 pounds down to 125 pounds, but in terrible health.

One thing is clear from this: thinner does not necessarily equal healthier! And BMI is a very poor indication of one’s health. As Rachel pointed out, according to some sources Tom Cruise has a BMI of 31, making him officially “obese.” Bodybuilders fall into this range or higher, too.

That’s because BMI doesn’t differentiate between weight from fat and weight from muscle and other lean body tissue! BMI is calculated only from your height and weight, period.

Did you know that you have an average to low BMI and still be overfat? There is a term used by many trainers to describe this: skinnyfat. When someone loses 175 pounds by dieting and doing endurance-style cardio exercise, she will lower her BMI but not necessarily increase her lean body mass.

That’s where resistance exercise comes into play. In order to increase your metabolism and be truly healthy, you need more than just a low weight. You need muscle! You don’t have to look like Arnold, either. Tom Cruise, Brad Pitt, and other leading men tend to be lean but strong. They have a gymnast or swimmer’s look, which most people find attractive.

When setting your fitness goals, ignore BMI. Ignore the number on the scale, for the most part. Set yourself a goal based on bodyfat percentage, and you’ll end up healthier in the end.

As for Rachel, she ended up increasing her calories, thus overcoming an eating disorder she had developed in her quest for an average BMI. She now weighs about 175, if I remember correctly. Unfortunately, I have no idea what she is doing for exercise, nor what her bodyfat percentage is.

For reference, here is a chart of bodyfat percentages. Remember that your own ideal body fat will depend on your body type, health, and goals.

FOR WOMEN:

Age Athelete Average Overweight Obese
20-40 yrs 12 – 20% 21 – 33% 33 – 39% Over 39%
41-60 yrs 14 – 22% 23 – 35% 35 – 40% Over 40%
61-79 yrs 15 – 23% 24 – 36% 36 – 42% Over 42%

 

 

FOR MEN:

Age Athelete Average Overweight Obese
20-40 yrs 4 – 7% 8 – 19% 19 – 25% Over 25%
41-60 yrs 7 – 10% 11 – 22% 22 – 27% Over 27%
61-79 yrs 9 – 12% 13 – 25% 25 – 30% Over 30%

 
I go into more detail about methods of measuring body fat in Methods of Assessing Fitness.

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Topics: Uncategorized | 5 Comments »

5 Responses to “What’s Wrong with BMI?”

  1. Vicham Says:
    March 21st, 2008 at 3:25 pm

    Nice chart. I wondered where I would fall in as far as my bodyfat % was concerned; nice to see it’d be average for my age. I always thought I was more on the overweight side, honestly!

    Now to work on getting towards that athletic number… 😉

  2. Stephanie Quilao Says:
    March 24th, 2008 at 1:41 pm

    I remember hearing about the skinnyfat situation years ago from a trainer. He said it was more common for women because women focus more on cardio and calorie restriction for weight loss and maintenance. But, I totally agree that skinny does not equal healthy.

  3. NEG Says:
    November 28th, 2009 at 12:26 am

    Hey, thanks for posting this. I just did my BMI & I’m 30.3, but I go to the gym everyday! & am not fat, tho I guess I’m “obese”

  4. Donna Says:
    July 26th, 2010 at 8:10 am

    Great website!! I especially love the article on the BMI. I make a similar point on my website. As an RN, I was taught to use the BMI in accordance with insurance assessment charts. Today I am a little more experienced and a lot wiser. The BMI is not accurate and we, as professionals, need to speak out against it. Good Job!

    **Donna

  5. FTBL 87 Says:
    November 4th, 2010 at 12:57 pm

    Ok, no matter what anyone says the BMI is not accurate for every individual. I am a Division 1 football player that is 6’5″ 230 lbs and my body fat is under 7 percent yet on the BMI chart I am overweight. Someone tell me i’m wrong, because i’m not…

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