Nutrition labels showcasing healthy foods have no significant impact on New Zealanders' food choices, according to latest research.
"Their effect is pretty small and limited to shoppers already interested in healthy eating," says leading nutrition expert, Professor Cliona Ni Mhurchu of the University of Auckland.
However, labels affect industry behaviour, with most labelled products reformulated to make them healthier (e.g. less salt, more fibre) as a result of adoption.
Ni Mhurchu, who headed research into the labels - known as Health Star Ratings (HSR) - says just over one in 10 of the 15,000+ packaged products on supermarket shelves carry the labels, making it difficult to create mass public awareness.
She believes the slow uptake by the food industry is because use of the labels is voluntary: "In my view, we need to get the number up to over half of all products - even two-thirds - to really make a difference.
"If we don't, then then I think we should look at making HSR mandatory."
Research into the labels - first used three years ago - was led by Ni Mhurchu through the Health Research Council-funded DIET programme. It involved 1357 New Zealand shoppers using their smartphones to scan food products in supermarkets.
Run over a year between October 2014 and November 2015, it found the labels had "no significant effect" on food purchases, although those who did use them liked the system, found them useful and easy to understand.
Backed by both the New Zealand and Australian governments, HSR offers shoppers a simpler way of determining the healthiness of packaged food than the detailed small print of traditional Nutrition Information Panels – a method many find difficult to read and understand.
HSR uses a star rating scale to measure nutrition content and healthiness. Ratings range from half a star to five stars (the more stars, the healthier the food) and is to be reviewed by both governments by the end of 2019.
Ni Mhurchu says by the middle of 2016 about 1000 products were carrying the labels, a number that has now risen to about 2500.
"It does seem slow," she says. "But I know it takes time to produce new packaging and we believe many in the food industry are reformulating some products [to make them healthier] before applying labels.
"Some industries have taken to it enthusiastically and the major supermarkets are now looking at using labelling for their own brand ranges. Big players like these will start to make a huge difference and, if we get wider uptake across New Zealand, then it will be a real win for everyone."
But Ni Mhurchu says part of the reason of the impact of the labels has been low is because Kiwis have a lot of other things on their mind when food shopping: "They are thinking about price and taste, so whether a product is healthy or not is often well down the list.
"I would like to see a bigger investment by the government in a social marketing campaign to support and promote the HSR labels."
"To work well, we must have the labels on lots of products so people can compare them. If they are only on some then people are only getting half the story – which leaves a lot of ambiguity."
She says while nutrition labelling is seen as one way to promote healthy eating, it is not by itself a silver bullet.
"It will complement other measures like healthier food in schools; labelling is a good way of deciding what foods should be available in schools or what foods are suitable to be marketed to children."
A 2016 Consumer New Zealand survey found 61 per cent of Kiwi consumers have seen the stars, while 75 per cent would like to see them on more products. Of those aware of HSR, 22 per cent refer to them often, 39 per cent sometimes with the rest (39 per cent) rarely or never using them.
The use of nutrition labels is also an issue globally. A 2012 Nielsen survey into world-wide food labelling trends, found 59 per cent of consumers have difficulty understanding labels on food packaging while 52 per cent said they understood the labels "in part".