If you're one of the many New Zealanders classed as overweight, you've probably been told your Body Mass Index is too high.
Body Mass Index (BMI) is the measurement of a person's weight in kilograms, divided by their height squared in centimetres.
It has been used to classify people as underweight, healthy, overweight or obese since the 1980s.
But is a maths equation really what doctors should be focusing on? Is it reliable?
A recent study by Annals of Internal Medicine found relying on BMI failed to determine risk factors for heart disease and diabetes.
The study suggested body-fat percentage was a better determinant of health, because it took into account whole-body composition (muscle, bone and fat).
All of the men in this picture have the same BMI. But they have wildly different bodies.
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All of the men in this picture have the same BMI. But they have wildly different bodies.
'Overfat' is a term that has jumped on to the dietary radar recently and refers to having too much excess body fat.
People who are overfat can be within a normal BMI range, but have increased risk factors for chronic disease, such as high abdominal fat.
So why do we still use BMI as our global measure of weight-related health? Would New Zealand's overall health look different if we changed the measurement?
Credit: Ministry of Health
Author of Fat Science, Dr Robyn Toomath, doesn't think so, and said BMI remained the best measurement we had.
"It determines what you should be for a particular height so for the vast, vast majority of us it works very well," she said.
"Because it's such a standardised measure it can be used not only for individuals but as an important public health measure. We need a stick in the sand to compare trends of populations."
Credit: Ministry of Health
The World Health Organisation continues to use the measurement to compare the health of countries, but mentions BMI should be used as a rough guide because it may ignore the amount of fat individuals carry.
The equation also cannot capture the tendency someone may have to develop type 2 diabetes.
"That's much more likely captured with abdominal fat - waist circumference measures that. But there's a lot more variability with waist circumference," Toomath said.
Ministry of Health deputy director of public health, Harriette Carr, said BMI was used as a global benchmark for health because it was an easy, consistent measurement.
"It's the most common measure of overweight and obesity used in research studies," she said.
The chance of developing diabetes and heart disease increases with higher BMI, and in 2016 the World Cancer Research Fund International found evidence people with a BMI classed as overweight and obese had an increased risk of many different types of cancer.
But there's also evidence that BMI ignores variation in physical characteristics.
"BMI may not be as accurate in highly muscular people or in ethnic groups with smaller body stature," Carr said. That's because people with smaller body frames typically carried more fat but may fall into a 'normal' BMI range.
In terms of alternatives, Carr said on an individual level, waist circumference should be used with BMI to provide an accurate assessment of weight - especially for those cultures that had smaller bodies.
But it's unlikely BMI would be fully replaced by another measurement any time soon. It was easy to calculate and had been successfully used for years to predict disease risk.
For now, it's the best we have.
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