What is BMI?
BMI is a numeric value calculated using a person’s weight and height. This value is then used to classify a person into one of 5 weight categories: underweight, healthy weight, overweight, obese, and extremely obese.
To calculate BMI, the CDC states, “Body mass index (BMI) is a person’s weight in kilograms divided by the square of height in meters” (1).
Using the metric system as described above, the formula would be represented as the following:
(2)
When using the imperial system of measurement, the formula is:
(2)
The results from these formulas are then interpreted by seeing which range the number falls into according to the weight classes.
Underweight: under 18.5
Healthy weight: 18.5 - 24.9
Overweight: 25 - 29.9
Obese: 30 - 34.9
Extremely obese: 35 and over
Is BMI useful?
Simply put, BMI may or may not be reliable for individual use, but can be very useful on a population scale.
BMI is not guaranteed to be an accurate representation of an individual’s health. Using only the values of one’s height and weight does not provide enough information to make definitive conclusions about health and body composition. For concerns about your own specific body, consulting an expert is recommended.
The primary purpose of BMI is for healthcare professionals to identify possible risk factors for health issues such as cardiovascular diseases and diabetes. These conditions are largely associated with obesity. Generally, BMI can act as a starting point for identifying the possibility of being obese and determining treatment.
(BMI is not intended to be a direct measure of body fat)
Given that all people have unique body composition, a single formula may not be accurate for everyone. A high BMI does not always equate to having too much body fat. For example, someone who has lots of muscle mass and low fat in proportion to their height could be calculated to have a high BMI. Muscle weighs more than fat, but this is not factored in during the calculation. This could then mistakenly imply that a muscular person is overweight or obese under the use of the BMI chart.
However, when used more broadly, BMI data is useful to public health experts who analyze obesity rates for a large sample size, such as for a community, city, state, or country as a whole. These statistics are more accurate across a broader range of people and can help show trends over time.
This is a practical method of measure on such a large scale because BMI is inexpensive, convenient, and quick. It doesn’t require any high-tech equipment and can usually be done on your own, meaning it doesn’t cost anything to figure out. All that is needed is numerical information, which allows for simple data collection. This data is very valuable to the public health field and leads experts into making the appropriate decisions on how to improve our health.
Sources: 1. About Adult BMI | Healthy Weight, Nutrition, and Physical Activity. (n.d.). CDC. Retrieved November 20, 2023, from https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html
2. Online BMI Calculator | Body Mass Index Calculator. (n.d.). Vertex42. Retrieved November 20, 2023, from https://www.vertex42.com/Calculators/bmi-calculator.html