Graphic health messages similar to those used on cigarette packets could be an effective way of helping people make healthier food choices, a study has found.
"We don't know yet if there's some messages that work better for some people than for others, there's still a lot more work to do," said study co-author Stefan Bode of the University of Melbourne.
"But in theory I'm very happy that it works at all because it's something that's easy to implement."
Whether we are likely to see scary images popping up on chocolates and chips anytime soon, however, remains to be seen, with other experts saying it's hard to know whether the results will translate to people's eating habits in everyday life.
The study participants were asked to rate on a scale how much they would like to eat each food at the end of the experiment.
Then they were shown health warnings. Some warnings were text only; others had pictures. Some had negative messages, such as "eating sugary foods increases your risk of tooth decay", while others were positive: "staying a healthy weight reduces your risk of heart disease".
Negatively framed warnings were more effective than positive health messages like this, the study found.
Supplied: University of Melbourne
After they viewed the warnings, the participants had another chance to rate a similar set of snack foods.
The researchers found using images combined with negative messages was the most effective way of persuading people to avoid the unhealthy options and choose healthier foods, they reported in the journal NeuroImage: Clinical and Appetite.
Positive messages with images were more effective than text-only messages.
The researchers also monitored the participants' brain activity with electrodes.
Dr Bode said there was a link between viewing the warning labels and activating their self-control, rather than acting on impulse.
"We can really see a signature of deploying this self-control to resist unhealthy choices," he said.
"This is something we're really excited about to follow up and see how this happens."
Lessons from cigarette packaging health warning campaign
The controlled nature of the study meant it was difficult to predict how people would respond to the health messages in real life, said Simone Dennis of the Australian National University.
Professor Dennis, who has researched the effectiveness of health warnings on cigarette packets, said people created workarounds, such as keeping their cigarettes in their handbags so they didn't have to look at the packaging.
Shock value can be an effective deterrent from unhealthy behaviours, but only for a short period of time, according to ANU Professor Simone Dennis.
Supplied: University of Melbourne
Professor Dennis wondered whether people would simply not look at the packaging, or tip the food into a different container to avoid seeing the health warnings.
"Using a series of very bland, unremarkable techniques that don't take a lot of imagination to do, but they are very effective," she said.
"It also means that they might not be as straightforwardly effective as these studies suggest, because they suggest that people will be confronted with these messages every single time they see the food."
Cigarette studies also showed health warnings were less effective in lower socioeconomic groups and Aboriginal communities, where the "particular middle-class value of health" the health warnings relied on did not resonate in the same way.
Professor Dennis also said the shock value of negative health messages had an expiry date.
Dr Bode hoped his research would see health warning messages become part of a broader strategy around helping people make healthy food choices.
But, he acknowledged, there was still more we need to know about what's happening in people's brains when they see the messages.
"What we can't say is can they work in real life, when they go to the supermarket and are bombarded with other messages," he said.
"We need to know, how long does this last? When do we need to time them?"