Missing the mark

The BMI is outdated, say experts who argue that focusing on health symptoms is more important than a target weight.

As a way of measuring whether someone is a healthy weight, the Body Mass Index (BMI) has its shortcomings. It would, for instance, put Dwayne "The Rock" Johnson and many of the All Blacks into the obese category, as it doesn't account for their musculature.

At the International Congress on Obesity in Melbourne last month, a group of experts drew on a growing body of research to describe how concepts such as "ideal body weight" or "normal" BMI are overly simplistic and don't tell you enough about the health of the person.

"The BMI measure [a mathematical formula that links weight with height] is really convenient," says one of those experts, Australian obesity surgeon Alex Craven. "But in terms of its accuracy, it's terrible at predicting whether people are going to get sick and die of this disease." Although obesity does increase the risk of metabolic health problems such as elevated blood pressure and type 2 diabetes, it is possible to have a high BMI and be completely healthy.