The Taxpayers' Union has declared its hand on which taxpayers it supports by becoming a virtual front group for the sugary drinks corporate taxpayers.

How can I tell? Just look at how they frame their arguments and what evidence they use to support them because it uncovers their motivations, intent and probably their funding.

In the Herald yesterday, Taxpayer Union economist Mac Mckenna laid out the arguments against a sugar tax and the headline conclusion that it will not make the nation healthier is already a dead giveaway about whose side they are on.

The first tactic Mckenna uses is to denigrate doctors and public health researchers by calling them "experts" and saying they are on a crusade and not using evidence. Generating rigorous evidence just happens to be our stock in trade, so his statement immediately looks like an alternative fact.

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Next, he sets up a straw man to knock down: if the goal of a sugar tax is to reduce obesity, then this needs to be proven beyond doubt and it isn't, therefore, there is no justification to implement the tax.

This is a standard tactic used by the beverage industry and governments which are ideologically opposed to sugar taxes. While they acknowledge obesity has no magic bullets, they demand magic bullet evidence for the policy they do not like.

New Zealand children will be waiting forever to have healthy food environments if Mckenna's yardstick of magic bullet evidence is applied to all potential interventions to reduce our appallingly high childhood obesity levels.

Mckenna then cherry picks some evidence to suit his arguments. This is easy to do, especially with many non-peer reviewed, industry-funded reports floating around to pluck some figures from.

Those of us who are seriously interested in what the totality of the evidence is telling us refer to systematic reviews of all available studies in the literature.

The most recent such review on sugary drinks tax was published last week by researchers from the University of Edinburgh who, importantly, are not industry-funded.

They analysed 80 studies which assessed outcomes from food taxes and concluded, "If the primary policy goal of a health tax is to reduce consumption of unhealthy products, then current evidence supports the implementation of taxes that increase the price of products by 20 per cent or more."

There you have it. The policy goal is reducing consumption of sugary drinks, not the straw man of singlehandedly reducing obesity, dental caries or depression which no one is claiming.

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Indeed, there is more evidence on the effectiveness of sugary drinks tax than there is for the entire 22 actions in the government's current childhood obesity plan. If evidence actually mattered in policy making, a sugar tax would be top of the list for preventing childhood obesity.

Mckenna then raises a potential concern which is that a sugary drinks tax will disadvantage the poor but lays down another alternative fact that, "Those who consume the largest quantity of soft drink are also the least likely to give it up."

Again some actual evidence helps. Two years after the Mexico sugar drinks tax, consumption in the low-income households is still down by 12 per cent compared with 5 per cent in the high-income households.

A recent modelling study in Australia estimated that half the health benefits of a sugar drinks tax would go to the 40 per cent lowest income households and the added tax cost to them would be only 73 cents per week more than high income households.

It is clear that people on low incomes, especially children, are the most responsive to taxes, reducing their consumption more than people on high incomes.

The outcome is, therefore, progressive and in fact we knew this already from tobacco taxes. Don't forget that obesity, diabetes, rotten teeth and depression are all highly regressive because they really hit the poor the hardest.

Finally, Mckenna's solutions for childhood obesity are very telling. Actually, he has no solutions other than to give the kids more information and let them choose what they want. He forgot to mention telling bad parents to do a better job.

Now instead of corporate taxpayers' value for money, let's follow the logic of a hypothetical Taxpayers' Union which was concerned about getting the best buys for reducing childhood obesity for the citizens' tax dollars. It would go something like this:

Unhealthy diets and obesity are costing taxpayers about a billion dollars a year, we know that a wide mix of strategies is needed to even make a dent in this, we noticed that just two months ago all countries, including New Zealand, at the World Health Assembly in Geneva endorsed a revised set of evidence-based, cost-effective policies to reduce obesity and diet-related diseases, we see that to "reduce sugar consumption through effective taxation on sugar-sweetened beverages" is one of the recommended policies which actually saves the health system money in the long term.

We go in to bat on behalf of citizens to make sure that a sugar drinks tax is a central part of a childhood obesity and nutrition plan. We join with other public interest groups, some of whom are taxpayer-funded, to try to get some real evidence-based action from a Government which is siding more with corporate wealth than children's health, so that we can save health dollars.

Of course, this hypothetical Taxpayers' Union does not exist because the song they are singing against sugary taxes is that of the corporate piper.

• Boyd Swinburn is professor of population nutrition and global health at the University of Auckland