For over 100 years, doctors, personal trainers and other health care professionals have used the Body Mass Index (BMI) to assess whether or not a person is overweight. But is this formula flawed?

How is the BMI measured?
You can measure your BMI by dividing your weight in kilograms with your height in metres squared.

    • A BMI of 18.5 to 24.99 means that your weight is normal
    • A BMI of 25 to 29.99 means that you are overweight
    • A BMI of 30+ means that you are obese.

How accurate is the BMI?
The current BMI formula leads to confusion and misinformation as the height² term divides the weight by too much when people are short and by too little when they are tall. The result is that short people are being told that they are thinner than they really are, while tall people are made to think that they are fatter than they are. The following example illustrates that the BMI also does not measure overall fat or lean tissue (muscle) content:

    • A couch potato is 1.83 metres tall, never does any exercise and weighs 92 kilograms. His BMI is 27
    • An athlete is an Olympic champion 100-metre sprinter, 1.83 metres tall, does an incredible amount of exercise and weighs 96 kilograms. His BMI is 28.

Clearly, the athlete is not overweight while the couch potato is; the athlete is far more muscle-bound than the couch potato and muscle weighs more than fat.

Is there an alternative to the BMI?
Calculation of your healthy weight depends on several factors including your overall general health, height, muscle-fat-ratio, bone density, body type, sex and age. However, many experts say that waist-to-height ratio is a better measurement than BMI and that you should keep your waist circumference to less than half your height.

In order to get a more accurate measurement of body fat to determine if a person is under or over weight, it is strongly recommended that the person visits a biokineticist who is qualified to do either the skinfold measurements or bio-electrical impendence. Other, more accurate ways to estimate the fat levels in your body include MRI and CT scans and measuring the levels of the hormone leptin in your body. However, these tests are expensive and time-consuming.

Conclusion
While the BMI is useful when studying large populations, it is not an accurate way of assessing whether individuals are overweight or not.

 

Sources
Nordqvist, Christian. 2013. Medical News Today. 31 January
www.natureworldnews.com