Body mass index (BMI) is likely to be an inconsistent measure of the risk of heart disease for Māori and Pacific people, a new study has found.
Otago University researchers looked at ultrasounds of hearts belonging to 205 Kiwis, measuring the amount of fat around the organ - the more you have, the higher chance you have of heart attacks and rhythm disturbances.
Of the 205, 164 were Pākehā and the rest Māori and Pacific people.
While there was a link between Pākehā participants' BMI - their weight in kilograms divided by height in square metres - and the amount of epicardial adipose tissue (EAT) around their hearts, no such correlation existed for Māori and Pacific people.
In fact, while the average Pākehā in the study had a BMI of 29.6 and the average Māori/Pacific person 31.8, the latter typically had a thinner layer of fat - 2.2mm to 1.8mm.
Lead researcher Sean Coffey says the measurements didn't match up, as doctors previously believed they would.
"When you look at the traditional measures of obesity or fatness, it's actually a pretty good predictor of what the EAT thickness is going to be - whereas for Māori and Pacific, that relationship just doesn't hold."
Dr Coffey says for them, it will need to be done differently.
"In New Zealand Europeans, you can make a pretty good estimate of it just by measuring BMI. But if you want to know in Māori and Pacific patients, you actually just have to do the scan."
The study, published in the New Zealand Medical Journal on Friday, notes previous studies have found Māori and Pacific people tend to be leaner than Pākehā with similar BMI scores.
"This has led to a call to move away from simple BMI measurements as an assessment of adiposity as part of such screening programmes as the B4 School Check."
The researchers note that by lumping Māori and Pacific people together in their analysis, differences between those two groups may have been obscured - but even with the small sample they had, there were no obvious differences between them when it came to EAT thickness and BMI.
"Our findings, in addition to previous research, indicate that the same level of BMI can carry different connotations of risk in different ethnic groups, with BMI likely being an inconsistent measure of obesity in Māori/Pacific patients," the study concluded.