Sugar-control campaigners are hailing research from Mexico indicating a reduction in purchases of sugary drinks on the back of the country's 10 per cent "soda tax".
They see this as vindication of their proposals to impose a similar tax in New Zealand to help control obesity and save lives and they urge the Government to adopt the idea with urgency.
Mexico is the second-most obese nation in the OECD behind only the United States. New Zealand is in third place with 31 per cent of adults obese.
In January last year, Mexico imposed an excise tax that increased the price of non-alcoholic and non-dairy drinks containing sugar by about 10 per cent.
Mexico's National Institute of Public Health and the University of North Carolina this week released preliminary results of their studies of the effects of the tax. They say purchases of sugar-sweetened drinks declined by 6 per cent on average last year and by 12 per cent in December.
The greatest reduction was among the lowest socio-economic group - 9 per cent on average for the year and 17 per cent in December.
"These are substantial, pro-equity changes," said Boyd Swinburn, professor of population nutrition at Auckland University. "New Zealand really needs to consider this evidence of impact and implement a similar excise tax here."
"It's one of the top three policies which are likely to have an impact on obesity."
Health Minister Jonathan Coleman was too busy with the Southern District Health Board's deficit to comment, but his Government has repeatedly ruled out imposing a sugar tax.
Greens health spokesman Kevin Hague re-iterated his party's call for a "levy" on sugary drinks to reduce their consumption - and thereby their contribution to obesity and dental caries - and to raise money for health promotion programmes.
He said the evaluation of the Mexican tax negated the Government's assertion of a lack of evidence of effectiveness of sugar taxes "and the Government should get on and act".
Food and Grocery Council chief executive Katherine Rich challenged the research. She said its method, relying on a panel of consumers, was less accurate than sales data.
"When I visited Mexico a few months ago I was told that consumption volumes from actual sales data are now back up to the pre-tax levels of a year ago after initially dipping."
In New Zealand, 17 per cent of the total sugar intake of adults - and nearly 30 per cent for males aged 15 to 30 - comes from non-alcoholic beverages. Researchers last year calculated that a 20 per cent tax on sugar soft drinks in New Zealand could save 67 lives a year from reduced ill health.
In Britain, a study estimated a tax of that size would reduce the number of obese adults by 1.3 per cent.
The Mexican tax
• Imposed in January last year
• Applies to non-alcoholic and non-dairy drinks containing added sugar
• Increased their price by about 10%
• Researchers say purchases declined by 6% on average last year
• Down 9% in the lowest socio-economic group