BMI is an acronym for body mass index. It’s one of the predictors of health. It uses your gender, height and weight to create a number. That number is represented on a chart to show whether you’re underweight, the right weight, overweight or obese. Since it’s a shortcut technique, it’s an approximation and not a totally accurate predictor of health. It’s a better predictor if used for people who don’t have a lot of muscle mass and doesn’t vary based on bone density.
It’s popular because it’s simple.
A doctor can quickly look at the BMI chart, even before he sees a patient, and judge the patients overall fitness with some degree of accuracy. The more overweight someone is, especially when they cross over to obese, the higher the potential for serious diseases, such as diabetes, cancer and heart disease. Being underweight also has its health risks, particularly for seniors. If that quick estimation was the end of the story, the potential for a misdiagnosis of overall health would be high. The doctor needs to see the patient first, to see why the BMI is high or low.
A body builder or championship wrestler could have a high BMI.
Muscle weighs more per cubic inch than fat does, so someone with extra muscle may seem slimmer than a person the same height, weighing the amount. If a person weighs 160 pounds and is 5’6″ his BMI would show he is overweight. If that same person were muscular, like a body builder, that extra muscle weight makes them healthier, and they don’t look obese at all. The elderly, pregnant women and people with a large frame and dense bones also present problems that make the BMI far less useful.
BMI may not be useful for cardiac health.
One study followed a group of individuals and concluded that BMI wasn’t necessarily a good predictor of cardiac health. It didn’t lead the doctors into predicting whether a patient would have a good cardiometabolic profile or not. A cardiometabolic profile includes cholesterol levels, blood sugar levels and blood pressure. That shouldn’t be surprising, there’s no one test or set of numbers that can predict every person’s overall health. Each person is unique and each test or set of numbers is just another clue in the person’s overall health.
- Newer types of measurements, like waist circumference, are more useful for predicting health and identifying obesity. Even though a BMI might not indicate obesity, a man with a waist over 40.2-inches or a woman with a 34.6-inch waist is considered obese with a higher chance of diabetes.
- One problem with other types of body density measurements, such as MRI scans and underwater weighing, is that they’re far too costly, but they do identify body volume, density and fat.
- Ironically, some of the fittest people, who have a lot of muscle, have been labeled unhealthy by insurance companies. To avoid paying extra for insurance, a picture of the person is often necessary, since many use BMI as a guide.
- RFM—relative fat mass index—is the technique that uses waist measurement as a health predictor. It uses a separate formula for men and women. For women, the formula is 76-(20 x height/waist circumference) and the male formula is similar, but uses 64 instead of 76 in the formula.
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