Research on the benefits of slicing sales tax off healthier foods has strengthened the Maori Party's struggle to introduce this policy.
The year-long study of 1100 supermarket shoppers found that those given a discount of 12.5 per cent - the level of the GST sales tax - on healthier foods increased the volume of these foods they bought by 11 per cent.
Fruit and vegetables comprised two-thirds of the increase.
But in a comparison group who were instead given advice on healthier options they could purchase, based on the foods they were routinely buying during the study at Pak'nSave supermarkets, there was no change in their quantity of healthier foods.
Despite the increase in healthier-food purchases, the amount of less-healthy food did not change. But the researchers said the increase in fruit and vegetables "represented an improvement in overall diet", because most people ate too little of these foods.
The increase in the discount group's healthier purchases was considered only a "modest" improvement, but it underscores the assertion of many public health practitioners and researchers, that to address the growing obesity rate, changing the food "environment" is more important than educational measures.
This position is in contrast to the Government's approach, which falls more on the side of education. National has also rejected the idea - pushed by the Maori Party and many in public health - of removing GST from healthy foods.
The Maori Party has drafted legislation that would introduce this policy, but it has not yet won selection from the ballot for member's bills.
"We're still lobbying the Government [on the policy]," a Maori Party spokeswoman said yesterday. "Even if National is going to say no, that doesn't mean the Maori Party is going to stop pushing for it."
The researchers, from Auckland and Otago Universities, say their findings show the importance of considering pricing interventions rather than relying exclusively on personal responsibility to improve diet.
The researchers suggest considering a range of policies, including removing GST from healthy foods, subsidising healthier foods, targeting subsidies to those on low incomes and giving subsidies to the producers and manufacturers of healthier foods.
Co-researcher Professor Tony Blakely acknowledged that removing GST from some foods would complicate the tax, but said many countries had some form of food-exemption system for their sales taxes.
* Discounts led to an 11 per cent increase in the volume of the healthier foods purchased.
* Advice on healthier foods had no effect.
Source: Auckland University and Otago University.