A sugar tax could have the unintended consequence of encouraging people to switch from sweetened soft drinks to booze, new research suggests.
And because wine and beer often have more calories than soft drinks, a poorly-targeted sugar levy could produce net neutral or even negative health outcomes, the researchers say.
"People don't just drink because they are thirsty. They drink socially. And you're not going to drink water in those circumstances - it's either sugar-sweetened beverages or alcohol. And that has not been considered in the debate in this country," says Dr Alan Barclay, a research associate at the University of Sydney.
Dr Barclay has attracted controversy in the past for claiming the link between sugar consumption and obesity in Australia is overblown.
But other researchers have questioned how much the study can really tell us.
A number of countries, plus several local jurisdictions in America, have imposed soft-drink taxes as evidence mounts linking drinks with high amounts of added sugar to a range of health problems including obesity and diabetes.
The UK will impose a levy on sugary drinks in April. Before that, researchers from the London School of Hygiene and Tropical Medicine and the University of Cambridge tried to model the levy's likely effects.
The researchers used purchase data from about 32,000 British households from 2012 and 2013. They tracked how much soft drink and alcohol they bought and the price they paid for it.
In a study published in the Journal of Epidemiology & Community Health on Wednesday, they found when prices for soft-drink were high, people bought less cola - and more booze.
A 1 per cent price increase for high-sugar drinks led to a 0.7 per cent drop in consumption, but also a 0.23 per cent rise in beer purchases.
However, the picture is mixed. A 1 per cent price increase in drinks with between 5 and 8 grams of sugar per 100 millilitres - moderately sugary - pushed down consumption of all beverages except spirits. The researchers term this a "health multiplier effect".
And the same price increase for diet soft-drinks led to sharp increases in wine and beer consumption and a steep drop in spirits consumption.
Dr Lennert Veerman, a public health expert at Griffith University, said the study was interesting but did not show price increases for soft-drinks directly led to more beer being purchased.
"It's an important topic. As you make some products more expensive you can expect shifts in the diet to occur, and it's important to monitor those so you have a net benefit.
"But this study raises more questions than it answers. Why would spirits consumption go down if the price of diet sodas go up? I don't take this to be any more than correlations that are anything more than interesting."
