Tag Archives: BMI

Muscle Mass Beats BMI as Longevity Predictor – Who Knew!?

Fit at 70!I’ve written a couple of times (here and here) about my dislike of the imperfect science of body mass index. In particular, I’ve stated that it does not accurately assess the elderly because of low muscle mass. The elderly are likely to have a “healthy” BMI despite being anything but. As people age they lose weight through muscle loss. This brings their BMI down and may even bring it into what is considered an optimal range. The problem is muscle mass loss reduces strength, which increases the likelihood of falls and a reduced ability to exercise. The last point is particularly problematic.

Now new research shows that when it comes to longevity, a focus on weight loss may be misplaced. Because BMI isn’t actually a very reliable indicator of life span. A more useful measure, some physicians say, might be muscle mass. Researchers analyzed BMI and muscle mass data from more than 3,600 seniors in a long-term study. And they tracked which seniors had died, a decade later. Turns out BMI wasn’t much good at predicting chance of death.

But muscle mass was: more muscle meant better odds of survival. The study appears in The American Journal of Medicine. [Preethi Srikanthan and Arun S. Karlamangla,Muscle Mass Index as a Predictor of Longevity in Older-Adults]. For more information see here.

Critics argue that it’s nearly impossible for the elderly to build muscle. I think they are missing the point. It’s not necessarily that the elderly need to bulk up. It’s that they need to minimize muscle loss. This is done through resistance training. Anyone, yes even the elderly, can resistance train. By doing so muscle loss is minimized. This may mean you don’t fit into the BMI scale perfectly, however, it does mean you are healthier. So, here’s to weight lifting!

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I’m Overweight.

Dr. C

Or at least you would think so if you looked at my body mass index (BMI). I have written about the very imperfect science of the BMI scale before here on my blog, but I thought it deserved to be revisited. BMI is basically a height to weight ratio that comes up with a number designed to make it easy for clinicians to decide if a person is overweight or obese. Before the BMI scale was invented it was hard to assess someone’s weight and say that it was appropriate because height is also an important factor in weight. BMI combined those two.

Calculating BMI is relatively simple. You need your weight in pounds and your height in inches. Take your weight and multiply it by 703. Take your height and multiply it by itself (height squared). Now divide the first number by the second number and you have your BMI. To see my calculations or do your own click this link. My BMI falls in the “overweight category” with a score of 26.2. However, my body fat percentage is about 18%. This is well within the acceptable range for a 33-year-old man. (And I clearly do not look overweight!)

BMI misses many things when calculating whether someone is at the proper weight.

The problem for some people, like athletes, it does not take into account muscle mass. A person that is heavily muscled will always be overweight according to the BMI. As a matter of fact, I have been considered “overweight” since college despite always being is relatively good shape. If we look at professional level athletes, most of them would be considered obese!

I understand that not everyone is an elite athlete. What about the elderly? BMI is not ideal for them either. In the United States that equates to about 43 million people. Many times an elderly person will fit nicely into the BMI by being considered “ideal weight” for their height. This can be significantly misleading. Why? In the elderly muscle mass begins to drop. It happens to all of us. However, with this drop in muscle mass comes a drop in weight. As weight is lost a person is likely to fall into the “ideal weight” category even though they should be concerned about muscle mass loss. This loss in muscle mass causes a loss in strength and stability, increasing the risk of falls and increasing the risk of osteoporosis. Another problem with muscle loss is the change in your body composition. As muscle mass is lost one’s body fat percentage increases. Body fat percentage is a great indicator of health. The lower it is (within reason) the healthier you are, generally speaking.

BMI also fails to take into account many other health factors like diet, exercise, inflammatory markers, nutrient status, stress load, chemical exposure, social well-being, mood stability, and a whole host of other things we know have a large impact on our health. However, it is still widely used as a primary assessment of one’s health. As I said, it’s an imperfect science. In my opinion, it’s so imperfect it should be eliminated.

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Body Mass Index – Don’t pay any attention to it

The Body Mass Index, or BMI,  is used to ascertain whether someone is overweight, obese or at the correct weight for their height.  It’s used by health professionals across this country as a guide for their patient’s health.  It’s wrong.

The reason for this blog is a conversation I had with a good friend of mine.  He also happens to own a gym and is a very talented and knowledgeable trainer/fitness coach.  We were discussing it in relation to his clients and my patients and how people are often times misled by the numbers they see when they use the BMI scale.

BMI was designed to be used as an easy tool for clinicians to assess their patients in terms of body weight relative to height. Before the BMI scale was invented it was hard to assess someone’s weight and say that it was appropriate because height is also an important factor in weight.  BMI combined those two.

How to calculate BMI:

The formula is simple.  You need your weight in pounds and your height in inches.  Take your weight and multiply it by 703.  Take your height and multiply it by itself (height squared).  Now divide the first number by the second number and you have your BMI.  Here is an example.  We’ll use my numbers.  I am 201 pounds and 71 inches tall.

201 lbs x 703 = 141,303
71 in. x 71 in. = 5,041
141,303/5,041 = 28.03

So my BMI is just over 28.  This puts me in the overweight category, actually moving close to obesity.  Wait…what?

If you look below you can see the classification system used for BMI.

You will see that anything above 30 is considered obese.  Technically anything above 29.9 is obese.  If we use this scale, I am only 13-14 pounds short of being considered obese.  People who know me will tell you that I do not look obese.  They will also tell you that I do not even look overweight.  So what’s the catch?

That is the problem with using BMI to assess health.  It doesn’t take into account many factors.

The problem for some people, like athletes, it does not take into account muscle mass.  A person that is heavily muscled will always be overweight according to the BMI.  As a matter of fact, I have been considered “overweight” since college despite always being is relatively good shape.  If we look at professional level athletes, most of them would be considered obese!

I understand that not everyone is an elite athlete.  What about the elderly?  BMI is not ideal for them either.  Many times an elderly person will fit nicely into the BMI by being considered “ideal weight” for their height.  This can be significantly misleading.  Why?  In the elderly muscle mass begins to drop.  It happens to all of us.  However, with this drop in muscle mass comes a drop in weight.  As weight is lost a person is likely to fall into the “ideal weight” category even though they should be concerned about muscle mass loss.  This loss in muscle mass causes a loss in strength and stability increasing the risk of falls and increasing the risk of osteoporosis.  Another problem with muscle loss is the change in your body composition.  As muscle mass is lost one’s body fat percentage increases.  Body fat percentage is a great indicator of health.  The lower it is (within reason) the healthier you are, generally speaking.

So does it work for anyone?  Yes, there are some people that it works for.  If a person is sedentary and eats a poor diet it may accurately depict your current weight status (ideal, overweight or obese).  There are, however, better ways to assess health.

Then how do I know if my weight is appropriate?

The best way to assess your weight status is to perform body composition.  This gives us a percentage number based on body fat.  For example, if you weigh 200 lbs and 50lbs of that is from fat, your body fat is 25%.  Below is the ideal body fat percentages for men and women.

The gold standard for measuring it is the caliper test or skin fold test.  A pinch of skin is precisely measured by calipers at several standardized points on the body to determine the subcutaneous fat layer thickness. These measurements are converted to an estimated body fat percentage by an equation.  It is most reliable when taken over time and it must be done by the same person to be accurate.  Techniques can vary from person to person and may change the results.

The other way to measure it by bioelectrical impedance.  You are hooked up to electrodes that are spaced far apart on your body; usually on each hand or on a hand and a foot.  An electrical signal is passed between the electrodes and the resistance to the current flow is measured.  This is a painless process.  Fat and muscle have different resistance rates so the machine can estimate the body fat percentage based on that.  It is affected by hydration levels so be sure to be hydrated when you take a test like this.  This is a very accurate method and does not depend on a person’s technique as the skin fold test does.

The best way to get your body fat to the desired level is a healthy diet and exercise.  You want to increase muscle mass and decrease fat.  This is done by weight training and short duration, intense circuit type workouts.  All of this can easily be done at any local gym.

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