A tax on sugary drinks could be introduced at $1 per litre, an Auckland University law professor suggests.

Stinging manufacturers and importers of sugary soft drinks is the best way to go about a sugar tax in New Zealand, a tax expert says.

"They would increase their prices, pass the burden on to retailers and wholesalers, and they in turn would pass the burden of tax on to consumers," Auckland University tax lawyer Michael Littlewood told a conference in Wellington on Tuesday.

That would be the most straightforward way to approach a sugar tax, he said.

FARFAX NZ Food and Grocery Council chief executive Katherine Rich says a sugar tax won't work.

"Manufacturers and importers are a relatively small number, and so the burden of compliance would be light."

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Littlewood proposed a per-unit tax on sugar, and suggested a $1 per litre charge would be reasonable and mean pricier, smaller cans of Coca-Cola were not targeted more than large, low-cost bottles.

He was speaking at a Wellington symposium run by lobby group Fizz, made up of a collection of researchers and doctors who want to eliminate sugary drinks from New Zealand by 2025.

But food and drinks councils are dead against the idea, and say a sugar tax won't work in the fight against obesity.

Despite regular soft drink consumption slowly declining, obesity continues to rise, according to research commissioned and released by the New Zealand Beverage Council and carried out by independent research company Nielsen.

"That means there are clearly other factors at play," president Olly Munro said.

The Food and Grocery Council agrees. Chief executive Katherine Rich said soft drinks were being used as a scapegoat for a complex problem.

"Taxing or banning sugar drinks won't work," Rich said.

Tackling obesity needed to concentrate on food literacy and moderation, rather than "blaming individual foods and drinks", she said.

"The present conversation is not getting us anywhere because it's particularly centred on attacking consumption of sugary beverages when the facts show there are many factors contributing to energy imbalance.

"You can't tax or regulate people slim."

Manufacturers were already front-footing sugar-related health problems by offering low-calorie and zero-calorie options, Rich said.

"In addition, our two biggest manufacturers, in partnership with the Government, have voluntarily refused to supply schools with sugar drinks for several years now."

FOOD TAX CALL

Morgan Foundation researcher and economist Geoff Simmons supported a sugar tax but said a "junk food tax" was what we should be moving towards.

"We are going to need a lot more tools in the case."

Simmons, who also spoke at the Fizz event, set out to debunk some of the arguments against sugar tax.

They included claims that its effects would be small, or would take a long time, Simmons said.

"I say, food industry, you've spent 40 years making us fat, you've got to give us 40 years to fix the problem."

Another argument centred around the effects a tax would have on poorer families, he said.

"It depends how you spend the money [collected from tax], that's potentially a massively progressive area. We know people on lower incomes are more likely to decrease their consumption in response to a price increase."

Health Minister Jonathan Coleman has been adamant the Government will not introduce a sugar tax until there is more evidence of it being linked to a drop in obesity.