University of Otago public health senior research fellow Dr Cristina Cleghorn analysed whether the scheme was improving New Zealanders’ health by prompting manufacturers to reformulate their products to gain better health star ratings.
The number of stars is calculated based on the energy, saturated fat, total sugar, sodium, fruit, vegetable, nut and legume levels of the food and in some cases, the protein and fibre content.
But Dr Cleghorn said there were gaps in the ratings system due to its voluntary nature.
"It does induce a small health gain, but because manufacturers and food producers can pick and choose the kinds of foods that the labelling gets applied to, it is having really mixed effects.
"So, they can just choose to put them on the healthiest foods to use it as kind of an advertisement for them, rather than what it’s designed for — which is to encourage people to choose healthier foods."
As a result, the labelling was not having as significant impact on what people were choosing as it could, she said.
"It really needs to be made mandatory in order to increase its impact."
People needed to be mindful the health star ratings only showed how healthy a product was compared with other similar products, she said.
"So, you really need to consider the kind of food that you’re eating ... It doesn’t tell you things like fruit is more healthy than chips, for example."
Modelling indicated the scheme had led to small changes in people’s diets, with sodium intake reduced by 18milligrams per person per day and fibre intake up 0.04grams per person per day.
"A company may change the nutrient content of that food in order to get a better star rating."
Dr Cleghorn’s findings were published in the latest issue of the Journal of the Royal Society of New Zealand.
The health stars rating system was introduced more than a decade ago after calls from nutritionists for better labelling of products.
New Zealand Food Safety deputy director-general Vincent Arbuckle said Australian and New Zealand governments might consider making it mandatory if uptake on intended foods remained well below the 70% target set for November this year.
A decision would be made by the relevant ministers following an assessment of uptake next year, he said.
"We consider health star ratings a useful tool, in conjunction with the mandatory nutritional information panel, to support consumer decision-making at the supermarket.
"They provide consumers with a simple front-of-pack rating that allows them to compare, at a glance, the overall nutritional value of similar packaged foods."
