Does your health care provider talk to you about your Body Mass Index (BMI) and do you know what it really means? Widely criticized as an oversimplification of a healthy weight, we discuss if BMI is a misleading metric.
BMI is a simple calculation developed by researchers that takes your weight in kilograms and divides by your height in meters squared (Kg/M2). BMI is classified by stages based on the World Health Organization (WHO) 2004 Guideline:
| BMI Range | WHO | Asian |
| Underweight | ≤ 18.5 | ≤18.5 |
| Normal weight | 18.5-24.9 | 18-22.9 |
| Overweight | 25-29.9 | 23-24.9 |
| Stage I Obesity | 30-34.9 | 25- 29.9 |
| Stage II Obesity | 35-39.9 | 30-34.9 |
| Stage III Obesity | ≥40 | ≥35 |
BMI offers two benefits that make it useful. It is easy to calculate, and it does not require special equipment. Additionally, it can be used anywhere with access to an online calculator.
However, when considering whether or not BMI is an accurate measurement there are several disadvantages to using the calculation to determine obesity. Firstly, it does not account for muscle mass; it cannot distinguish between bad fat and good fat and it does not account for ethnic variations of obesity. For example, a person that lifts weights such as a football player may be mistaken for obese due to their large muscle mass and a person with higher belly fat may be considered normal.
In 1994 the World Health Organization and the National Institutes of Health set obesity guidelines based on data from European and Caucasian Americans. As a result, this data did not account for other races or ethnic groups globally because there was no data available. In 2004 a guideline for Asians using data from Thailand, China, Hongkong, Singapore and Korea were used to give Asian guidelines. However, South Asians were left out, as well as African, Middle Eastern peoples. Much work remains to be done to produce more accurate BMI guidelines that can be applied to more people globally as well as nationally in the United States.
So, is BMI a good indicator of health? Certainly, it can be a gauge to measure excess weight, but not the ultimate indicator of obesity or of achieving a healthy weight. It should be used together with other tools to measure obesity. Waist Circumference is an important measurement and Body Composition machines can also be a helpful tool when available to guide weight loss. Assuredly, your fat to muscle ratio is more important than BMI alone. So, do not get stuck on thinking you should have a certain BMI, there is more to the story than this generalized number.
BMI calculators:
Adult BMI Calculator | Healthy Weight, Nutrition, and Physical Activity | CDC
Asian BMI Calculator (joslin.org)