More people are starting to question the accuracy of the BMI (body mass index) measurement. Essentially, this is a measure of your weight to height ratio. Maybe this formula is outdated going back to Lambert Adolphe Jacques Quetelet’s 1832 development (your weight in kilograms divided by your height in meters squared). Popularity didn’t strike until the 20th century when insurance was being evaluated for risk potential and among specific populations.
Formula:
U.S. units: Weight in pounds ÷ height2 in inches) x 703 = BMI (for example: 150 pounds ÷ 65 inches2 x 703 = 26.6)
Metric units: Weight in kilograms ÷ height2 in meters = BMI (for example: 70 kilograms ÷ 1.7 meters2 = 24.2)
| BMI | Weight Classification |
| Below 18.5 | Underweight |
| 18.5-24.9 | Normal |
| 25.0-29.9 | Overweight |
| 30.0 or higher | Obese |
Generally, yes, BMI does stay true to the trends. Patterns show those below the line are healthy and those over the line are not. Predictions of disease and mortality due to poor health can be documented and charted. Of course, with any measure, this doesn’t hold true for ALL. Therein lies the complication. There are some variables to consider. A person with more lean muscle mass and less fat mass might measure in the overweight category. Age is a factor because most older adults do have more body fat than lean muscle mass. That is a normal ageing factor, but the measurement would show in the overweight category.
Race and ethnicity can be confusing. For example, even though Asian and Middle Eastern people may have a lower BMI, this doesn’t mean they are not at risk for health conditions. Mexican American women tend to have higher body fat than white or Black women. Black women have less metabolic risk even with a higher BMI compared to white women. Therefore, lumping all races and ethnicities into the same categories can be complex. Weight distribution also should be considered. There are apple shaped and pear-shaped bodies. These body types may weigh the same, but the person who carries more weight in the stomach area is at higher risk for poor health.
BMI is an easy formula not requiring equipment or fancy scales. Other measures like lean mass versus fat mass may be more accurate for purposes of looking into health risks, but this can be expensive. Waist circumference is hard to measure with very obese people. In the end, BMI is a broad number with many variables, so it should not be the sole determinant of health risks nor the only indication used to tell someone they are unhealthy. Data and labels are scary and should be taken with caution. Always look at the whole picture, not just one number. In other words, BMI goes well with a second opinion and more information.
Megan Johnson McCullough, Ed.D, owner of Every BODY’s Fit and Mindful BODY’s Recovery in Oceanside CA, is a NASM Master Trainer, AFAA group exercise instructor, and specializes in Fitness Nutrition, Weight Management, Senior Fitness, Corrective Exercise, and Drug and Alcohol Recovery. She’s also a Wellness Coach, holds an M.A. Physical Education & Health, and Ed.D in Health and Human Performance. She is a professional natural bodybuilder, fitness model, and published author.
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