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!
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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