Body Mass Index (BMI) is the magical term that is often thrown around many readings that focus on exercise and wellness. You may have also heard your GP and other various specialists mention it.
What is a BMI?
Put simply, it is the relationship between your weight and height. It is a great baseline indicator of an individual’s general health – it classes people into the categories of underweight, healthy, overweight and obese (this is further divided into class 1, class 2 and class 3 depending on severity. It is generally accepted that a higher BMI ranging into the overweight categories puts an individual in the more-likely category for conditions like cardiovascular disease, hypertension and diabetes.
However – the BMI reading of an individual should not be taken as gospel and used to categorise a person. Why? Read more below:
As mentioned above, a BMI reading is very generalised. It does not account for what is actually making an individual’s weight read as what it is. For example, some of our rugby players are very tall and muscular. Richie McCaw of the All Blacks Rugby Team has a BMI of over 30kg/m2. This would place him in the obese category, but Richie is an international athlete and is incredibly fit!
Conversely, many seniors and other sedentary people tend to lose muscle mass due to not being active. This could then result in a lower weight reading and therefore a BMI reading in the underweight-healthy range, but that does not necessarily mean the individual is healthy! It is important to ascertain what the weight reading of an individual is composed of and perform other tests to determine their other health markers.
In addition to not being able to determine if an individual is heavy due to muscle or not, a BMI does not tell us where fat is placed on an individual’s body. Fat is not a bad thing! Our body needs it for warmth and also certain types of hormone regulation. However, where the fat deposits are on our body can dictate our predisposition for developing chronic conditions.
Fat around our buttocks and thighs, whilst not being allowed to spiral out of control, can have a good impact on metabolic disease as it tends to be more subcutaneous fat which secretes certain hormones. However, fat that is generally stored around the waist and stomach is primarily the ‘deep’ visceral fat that wraps around your organs and can really increase your risk of chronic conditions developing later! We need to be able to ascertain where in the body the fat deposits are by utilising other assessment tools, such as taking waist circumference or using skin-fold callipers.
A BMI reading is not a bad assessment tool and should not be discarded as useless. We just need to ensure that alongside a BMI calculation, we employ other methods of assessment to determine our health.