With different heights, weights, and body types, it is difficult to find a uniform measure of whether a person is overweight or obese. The Body Mass Index (BMI) was developed to create such a measure, basing a person’s healthy weight on their weight in relation to their height. While there are some arguments that the BMI still does not capture a person’s true healthy weight, it does give a good ballpark figure to determine if someone is getting close to obesity, is quite obese, or possibly too far underweight.
HOW THE BMI WORKS
The Body Mass Index measures a person’s weight in accordance with their height. There are many calculators online to do the math, but primarily it is a calculation of weight and height. In the metric system, it is calculated by weight in kilograms divided by height (in meters) squared. In imperial units, the calculation is weight (in pounds) multipled by 703, divided by height (in inches) squared.
CLASSIFICATIONS IN THE BMI
When a person receives their BMI value, it will typically be a number between 16 and 33. The following is a breakdown of categorization:
BMI 18.5 25 30
POSSIBLE COMPLAINTS ABOUT THE VALIDITY OF THE BMI
One of the primary complaints is that the BMI measures total mass and infers the proportion of muscle to fat. However, muscle weighs more than fat, so a person with a lot of muscle and very little fat might easily misinterpret their BMI. They could, for instance, fall into the “obese” category when they are, in fact, just strong. This argument is countred by BMI proponents who say that any weight over the average, be it muscle or fat, still can put a strain on joints, the heart, and other parts of the body usually affected by obesity, and thus a higher BMI is still a problem. Athletes, for example, are better off measuring body fat rather than BMI.
Another complaint is that the same scale is used for men and women, when women biologically have a higher percentage of fat in their body (usually in excess of 15%). In addition, no control is given for age, despite the fact that the healthy weight for a human changes as the body gets older.
In conclusion, while there are certainly some shortcomings to the Body Mass Index, it provides a good general indicator of obesity or being underweight. However, as in any matters of health, a doctor should be consulted before any measures are taken as a result of a BMI reading.
Sources: Department of Health and Human Services, http://www.nhlbisupport.com/bmi/.
Centers for Disease Control and Prevention (CDC), http://www.cdc.gov/healthyweight/assessing/bmi/.