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Should we be using BMI as a measure of health? 

Monday 18 July 2022 8:25am

EDOR Co-Director Professor Jim Mann talked with Emile Donovan from Newsroom's The Detail (hosted by RNZ) to explain why we still use Body Mass Index (BMI) as an indicator of health.

BMI is a measure of a person's weight in proportion to their height and gives an estimate of whether an individual is carrying excess body fat. There has been a lot of publicity around the limitations of using BMI in certain populations, but does this mean that BMI is not useful at all? 

During the interview, Professor Mann highlighted that BMI is still important for determining health at a population level. 

"It [BMI] is a reasonably good indicator of body fatness at a population level, and body fatness at a population level is one of the major determinants of health in a country or internationally."

Professor Mann stated the BMI can also be useful in the clinical setting for identifying people at risk of health issues. There are limitations though, when looking at BMI at the individual level. Other health indicators such as blood pressure should be assessed as well. 

Why is BMI controversial?

The limitation of using BMI for measuring body fat in athletes is often used as a reason to dismiss using this measure in the clinical setting. This is because the BMI calculation cannot differentiate between weight from fat and weight from muscle. Therefore healthy individuals with high amounts of muscle, such as rugby players, can be misclassified as having obesity.

However Professor Mann highlighted that there are only a small proportion of people in Aotearoa New Zealand with such a high muscular development, and the majority of people in NZ do not fit into this category. BMI should not be set aside simply because of this limitation. 

BMI is a simple measure that can be used by health professionals to start the conversation with people about their health. With around 1 in 3 New Zealanders over the age of 15 considered to be living with obesity, Professor Mann believes it is vital that excess body fat is not dismissed but is addressed as a health issue. 

 "We cannot ignore the problem of obesity - we ignore it at our peril."

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