BMI scale - How accurate is it?

Using the Body Mass Index (BMI) scale to check if you're overweight should not be taken as gospel, an academic says.

A new Otago University study has found two million Kiwis will be considered obese by 2038 if the current obesity epidemic isn't curbed.

Research published today in the Australian and New Zealand Journal of Public Health shows the average BMI went from 26.4 to 28.3 between 1997 and 2015. 

At that rate, by the early 2030s it will cross over the obesity threshold of 30.

So how much weight should we be putting behind the BMI calculators?

A simple Google search will help you measure your BMI on one of many available calculators by simply punching in your height and weight.

However Dr Ross Wilson, who led the research, says while online calculators can be somewhat useful, you shouldn't live by what they say.

"They can be useful for people wanting to get a general idea of their overall health but shouldn't be taken as gospel," he says.

"It doesn't capture everything about a person's health, but it can be useful getting a general idea."

If people are concerned about their online BMI measurement they should contact their doctor who can take a more complete examination of their health. 

Dr Wilson said there are specific limitations when it comes to the online calculators. 

High performance athletes will lean towards the higher end of the BMI scale as muscle weighs more than fat, he says.

Using that theory, Newshub found this to be true. 

Twenty two of the 23 All Blacks who ran out against France last month in Auckland are either overweight or obese. 

In fact, the entire front row was classed as obese.

Fitness coach Reuben Thompson isn't convinced of his BMI. He eats healthily and trains six times a week, but is classed as almost obese.

"It doesn't base it on your current activity, your nutrition, your daily lifestyle. So these are a lot of key factors to find out whether you are in a healthy state."