Most of us have probably heard of body mass index (BMI) and maybe even calculated it. If you’re curious what your BMI is, simply google a BMI calculator, or if you have a calculator, the calculation weight (kg) divided by your height (m) squared. Here’s a little bit about it and some important things to know when calculating BMI:
What is BMI?
BMI is a measure of the relationship between your weight and height. This can then be compared to 4 categories - underweight, normal, overweight and obesity. The obesity category is further divided into 3 classes:
Underweight - 18.5 kg/m2 or below
Normal Weight - 18.5-24.9 kg/m2
Overweight - 25.0-29.9 kg/m2
Obese - 30.0 kg/m2 or above
Class I - 30-35 kg/m2
Class II - 35-40 kg/m2
Class III - 40 kg/m2 or above
What is BMI used for?
BMI is used as a screening tool for disease risk factors but it DOES NOT diagnose how “fat” or unhealthy someone is. This is an important distinction as you will see BMI is not always accurate.
What is BMI useful for?
Generally, a higher BMI is correlated with a greater risk for developing certain conditions such as diabetes and high blood pressure and can be an effective tool to help determine risk factors for these diseases/conditions.
Where does BMI fall short?
At the expense of a simple calculation, BMI does not take everything into consideration. For one, women tend to have more body fat than men. People of different ethnicities also have different levels of body fat which can impact BMI calculations. Elderly people are often mis-categorized due to reduction of bone and muscle due to aging. Athletes are also widely mis-categorized largely due to muscle being heavier than fat. As the BMI categories are not divided by sex, race, age or athletic ability, the calculation may not always be accurate. BMI also doesn’t separate lean body mass and body fat mass. Lean body mass includes water, muscle, bones, skin and organs. BMI just considers your total body mass and combines lean and body mass together.
Interesting fact: Lebron James’ BMI classifies him as overweight. Those who know who he is will know that he is extremely muscular and you would probably not consider him overweight. This goes to show the limitations of the BMI calculation.
Final Thoughts
BMI is still a useful tool to use to determine risk factors for certain diseases, but it is definitely not a diagnosis of a certain level of health or “fatness”. People with a normal BMI can also be “unhealthy”. It is still good to be aware of your BMI but also realize that it has its limitations and doesn’t factor in everything. Classifying yourself through 1 test is not the best indicator of your health and other tests such as waist circumference and lean mass calculations can provide a better insight to your health but again; also have some limitations. At the end of the day, it’s your body and you make your own health decisions. Being happy with your body is key, strive to meet your health goals and be the best version of YOU!
Sources and Further Reading
Nuttall F. Q. (2015). Body Mass Index: Obesity, BMI, and Health: A Critical Review. Nutrition today, 50(3), 117–128. https://doi.org/10.1097/NT.0000000000000092
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