"Most crucially, the recent Berkeley, USA study showed clearly that a tax of one per cent per 30gm decreased consumption of SSBs in low-income communities and increased consumption of water."
A tax of 20 per cent has been shown to work, Potter advised, but should be based on volume or sugar content, not value.
"Reduction of consumption via a tax will probably be greatest among the households with the lowest disposable income. In New Zealand, Māori and Pacific will benefit strongly," Potter, a professor at Massey University's Centre for Public Health Research, wrote.
Over time a tax could save 50 lives a year and save at least $6 million in health costs, the briefing stated. It would raise about $40m in revenue.
Potter advised a sugar tax could be an evidence-based "anchor" in a comprehensive strategy, including restrictions on marketing to children, education and safer biking routes.
Sir Peter Gluckman, until recently the Prime Minister's Chief Science Advisor, told RNZ in June that the evidence for a sugar tax in countries like New Zealand had become much stronger. A report to Ardern had outlined that change, he said.
The Herald asked Ardern's office for that report. In response, the briefing by Potter was released.
"This briefing was requested to provide background following media interest in the issue," her office wrote. "It should be noted that the Government is not actively considering a tax on sugar or sugary beverages at this time."
Much of Potter's briefing matches his earlier advice on a sugar tax.
Sugar tax opponent Eric Crampton, chief economist at the New Zealand Initiative think-tank, said the briefing showed Gluckman appeared to be on very weak ground in claiming the evidence had become stronger.
"The only evidence to which his office can point is a brief and poorly documented note from the Ministry of Health's chief science advisor Dr John Potter. That note does not even mention the existence of the ministry's very recent commissioned review, released only a month before Dr Potter's note, that drew the opposite conclusion."
Crampton said that review, completed by NZIER, concluded there is very limited evidence that sugar taxes have been effective in cutting consumption and improving health.
"They found that the more rigorous studies found effects too small to plausibly generate health benefits."
On quick examination, it appeared much of the work cited in Potter's briefing was already covered in the NZIER review, including Berkeley's soda tax, Crampton said.
"It seems misleading to fail to mention the fairly comprehensive review undertaken."
In February the Herald revealed Andrew Blair, chair of both Capital & Coast and Hutt Valley DHBs, had written to Health Minister David Clark, urging him to bring in a tax.
"For the first time in history, NZ children could live shorter lives than their parents as a result of excess weight and obesity," Blair warned.
In response, Clark said the Government had promised no new taxes this term and was instead working with industry to bring down sugar content.
