Overweight on a BMI Chart?
The BMI Index May Not Be an Accurate Measure of "Overweight"
Oct 21, 2009
People who have a BMI over 25 are considered overweight. But what does that actually mean?
The BMI refers to the body mass index, defined as an individual’s body weight divided by the square of their height.
The BMI is supposed to help give an estimation of how healthy a person is based on their weight. While a person’s BMI can be calculated quickly and without expensive equipment, the index isn’t as accurate as it could be. Since BMI is only concerned with total weight, it doesn’t take into account frame size or muscularity. Many athletes have a BMI index that would put them in the “overweight” category because of their weight—from all that muscle. Because muscle density, bone density and body frame are not taken into account, some individuals can have a BMI of less than 25 and still be considered overweight by other measures, while others may have a BMI that is significantly higher without falling into that category.
The BMI was invented between 1830 and 1850 by Belgian Adolphe Quetelet as part of his attempt to develop “social physics.” It became popular in the early 1950s and 60s when Western society became prosperous enough to develop obvious obesity trends. The BMI made it easy for people to be categorized—or categorize themselves—as super skinny (underweight), normal, or fat (overweight or obese). It was never the BMI’s purpose to serve as an actual diagnostic tool, but simply as an easily referenced guideline.
Furthermore, the category lines of what is “healthy” and what is “overweight” might not actually reflect those realities. In 1998, the US National Institutes of Health changed the healthy/overweight category line from a BMI of 27.8 to a BMI of 25 to bring their guidelines in line with the World Health Organizations guidelines. This automatically re-categorized approximately 30 million Americans from “technically healthy” to “technically overweight.”
Different countries also have different guidelines. Southeast Asian guidelines put the cut off at a BMI of 23 in order to adjust for the Southeast Asian body types.
In the end, a true definition of “overweight” is having more body fat (adipose tissue) that is optimally healthy (30 percent body fat for women and 25 percent body fat for men). Body fat measurements such as skinfold calipers (the pinch test) can provide more accurate estimations of total fat percentage in the body, as can more expensive tests including bioelectrical impedance analysis, hydrostatic weighing and dual energy X-ray absorptiometry. Even taking their measurements can help determine if they are healthy by determining how they store fat. (Where people store it can change their health risks).
While the BMI is not a perfect tool, most people—non-athletes and those with average body frames—can still use it to approximate their weight category. But it shouldn’t be the only measurement of health. Body fat percentages, fitness tests, and doctor’s physicals are better ways to determine if someone needs to lose weight or not—and how much weight they need to lose in order to be healthy.
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