What is the body mass index (BMI)?
Simply put, the body mass index (BMI) is a measure that uses your height and weight to work out if you are a healthy size and calculate your BMI measurement.
Your BMI is found by dividing an adult’s weight in kilograms by their height in metres squared. The resulting number- usually between about 15-40 shows whether that person is underweight, a healthy weight, overweight or obese.
For those aged 2 to 18, the BMI calculation doesn’t just take into account their height and weight. Their age and gender are incorporated into the equation as well as.
A healthy BMI is in the 18.5 to 24.9 range for the majority of adults. This is definitely the case in individuals with a normal musculature.
The ranges measure in at:
below 18.5: underweight
between 18.5 and 24.9: healthy weight
between 25 and 29.9: overweight
between 30 and 39.9: obese
over 40: severely obese
Accuracy of BMI measurements
There are some great benefits to the BMI formula. It takes natural variations in peoples’ body shapes into account, allowing a healthy weight range according to their height. In giving an absolute reading that can be applied across the board in this way, BMI measurements supply very useful data from which healthcare and fitness professionals can take their cues.
That being said, there are several other factors that need to be taken into account when deciding how overweight individuals actually are. For many people, a BMI reading may not prove an accurate testament to their body fat levels.
Muscle is far denser than fat. As a result, very muscular people, such as bodybuilders and certain athletes, may have healthy body fat levels even though they would be classed as obese by their BMI measurements. This is because they will have extra weight in the form of muscle.
People with above average levels of muscle mass should therefore be cautious when working out their BMI- it will no doubt be higher than their body fat levels might suggest.
In addition, BMI should not be used as a measure of weight during pregnancy- when you’re expecting, you’re meant to be heavier than normal in relation to your height!
Always seek the advice of a qualified healthcare practitioner if you're in any way concerned about your weight.
Should we be using BMI?
Yes! It’s a good rule of thumb for most people. Untrained individuals, endurance athletes and gym-goers not focussed on hypertrophy will all benefit from knowing where they place on the scale.
It will tell those who need to put weight on that they are underweight, objectively signalling to those with eating disorders such as anorexia or bulimia that their bodies are undernourished. Likewise, it will signal to those over a BMI of 25 that they most likely need to lose some body fat.
BMI calculations are a fantastic tool for determining how healthy somebody’s body weight is.