What Is BMI?
The Centers for Disease Control and Prevention (CDC) defines body mass index as "a measure of weight adjusted for height, calculated as weight in kilograms divided by the square of height in meters." It was developed about 200 years ago by a mathematician named Adolphe Quetlet. Originally called the Quetlet Index, the goal was to aid the government in measuring the degree of obesity of the general population.
The CDC defines BMI ranges and their corresponding weight statuses as:
- Below 18.5 -- Underweight
- 18.5-24.9 -- Normal
- 25.0-29.9 -- Overweight
- 30.0 and Above -- Obese
Is BMI the Best Tool?
The measurement is simple, inexpensive, and noninvasive, which has contributed to its increased use. The CDC states that a “high BMI can indicate body fatness." However, the key word being “CAN” typically refers to the “general” population. In health care one needs to take into consideration the athleticism of the individual. The BMI equation has no way of measuring the density of fat mass versus free fat mass (basically everything else in your body, including muscles, bones organs, tissue and fluid). This means that someone with strong bones, well-developed muscle tone, and low fat mass could still have a high BMI. This is also to say that someone with insufficient bone density, low muscle mass, and moderate to high fat mass could fall into the “healthy” range.
What Health Concerns Can be Helped through BMI
There is research to support that all-cause mortality and cardiovascular disease (CVD) risk was decreased in individuals with a moderate to high physical activity level despite a BMI considered overweight or obese. A 2008 study published in the International Journal of Obesity reviewed a selection of measures that are more accurate at determining body fat than BMI. These include:
- Skinfolds, where skin and fat thickness are measured away from the muscle to determine body fat levels
- Bioelectrical impedance analysis, which uses electrical signals to measure the body tissues' resistance (fat is more resistant)
- Hip circumference
- Waist-hip ratio
- Sagittal abdominal diameter, which measures the distance between the back and the highest point of the abdomen
- Dual-energy x-ray absorptiometry (DEXA), which uses body scans to measure bone density and fat content
Also, according to the CDC, another simple measure of body fat distribution is waist circumference (sometimes divided by height).
Although the BMI is a quick and easy tool commonly used in health care, it is important for the health care community to assess each patient as an individual and not use the BMI as a blanket assessment tool.
Can BMI Measure Health and Wellness?
The main takeaway concerning BMI is that it should not be used as a measure of an individual’s health and wellness. Health is a culmination of habits and behaviors that you practice most days, such as: eating a balanced diet of mostly lean proteins, vegetables and fruits, coupled with moving your body, drinking adequate water (at least 64oz), and managing stress levels . If you are worried about your health, focus less on the numbers and more on the habits you do each and every day currently that support your health and wellness.
Reach out to the CHI Health Weight Management department for more questions.