Don’t get hung up on your BMI (Body Mass Index)

The usually reliable WebMD has a very nice quiz on fat that I recommend you take. It’s fun and can fill you in on some aspects of body fat that most folks don’t understand.

Having said that, I would like to take exception to the final question in the quiz which asks which BMI category is healthier? Anything below obese; The low end of normal; Anything in the normal range.

I wish we would do away with the BMI as a tool in evaluating fitness, health, fatness, you name it.

First of all, a lot of people think it tells them their percentage of body fat. It doesn’t. A person’s BMI is calculated as her weight in kilograms divided by her height in meters, squared.

It is an index, not a body fat measurement.

The readings are as follows: Underweight: less than 18.5; normal weight 18.5 – 24.9; overweight 25 – 29.9; obese BMI of 30 or more.

Second, it doesn’t take into account where the fat is distributed on the body. Fat around the belly is much more dangerous than fat elsewhere.

Arnold Schwarzenegger as Conan the Barbarian. Six foot two inches tall, 257 pounds, BMI 33 - obese?

Arnold Schwarzenegger as Conan the Barbarian. Six foot two inches tall, 257 pounds, BMI 33. Not what most of us would call obese.

“The usefulness of BMI is not great when considered on an individual-to-individual basis. In practice, BMI is most appropriate for large sample populations or in a clinical situation to quantify risk for a patient who is clearly overweight and overfat at the same time,” according to Professor Michael J. Ormsbee, creator of the Course Changing Body Composition Through Diet and Exercise which I am taking.

Dr. David Edelson, MD, writing for the Obesity Action Coalition  says, “…there is no accounting for differences in body frames, or even more importantly, body composition.

“BMI, while being a reasonable estimator of obesity in someone of average conditioning, becomes a terrible predictor in people with either lots of lean muscle (trained athletes) or very little lean muscle (severely de-conditioned individuals). BMI does not tell you anything about what is going on inside someone’s body, which is what we ALL should really be interested in.”

Keith Devlin, on National Public Radio, gave “10 reasons why BMI is bogus

His first reason is “The person who dreamed up the BMI said explicitly that it could not and should not be used to indicate the level of fatness in an individual. The BMI was introduced in the early 19th century by a Belgian named Lambert Adolphe Jacques Quetelet. He was a mathematician, not a physician. He produced the formula to give a quick and easy way to measure the degree of obesity of the general population to assist the government in allocating resources. In other words, it is a 200-year-old hack.”

You can read the remaining nine reasons at the link.

I have written about belly fat several times – How bad is extra belly fat?, What about belly fat – central obesity?

In addition there is: What is a good way to measure body fat?

I think you are a lot better off with this tool than the BMI.

Tony

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7 Comments

Filed under belly fat, fat, Weight

7 responses to “Don’t get hung up on your BMI (Body Mass Index)

  1. Reblogged this on One Regular Guy Writing about Food, Exercise and Living Past 100 and commented:

    I thought it might be timely to take another look at BMI (Body Mass Index) as we enter the holidays and we battle the bulge at holiday parties, family dinners, etc.

    Like

  2. salbers12

    Tony,

    Since Cancer is one of the major killers, minimizing Cancer risk seems a really good idea. Some of the best research comes from the American Institute for Cancer Research which has published 10 guidelines:

    http://www.aicr.org/reduce-your-cancer-risk/recommendations-for-cancer-prevention/

    Its #1 guideline is “be as lean as possible without being underweight”. This equates to BMI of slightly above 18.5; verified by a huge volume of Cancer research. This means that the BMI measurement is extremely valuable for avoiding Cancer. The implications of this are profound and spill over to other chronic diseases as well.

    Liked by 1 person

    • Thanks for sharing, but I think it is more important to know your body fat percentage than to worry about an index like BMI. I stand by what I quoted professor Ormsbee as saying in the post, the BMI number is good when discussing large populations, not individual’s health considerations.

      Like

      • salbers12

        AICR can supply a volume of study data that correlate individual BMI with Cancer. Logically, BMI should not correlate as well to large populations as it does for individuals since outsize individuals in a large cohort demonstrably compromise results. But I’d be willing to keep an open mind and review the basis of Professor Ormsbee’s claims.

        I do agree on the potential value of underappreciated % bodyfat. But the gross number is not a complete picture. Where the fat is located plays an important role. A major percentage of the population is skinny on the outside and fat on the inside. The only way to depict fat location is with sophisticated scanning technologies.

        Liked by 1 person

      • I agree that body composition is key.

        Like

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