The idea of a sugar tax is back on the agenda.

This time, it's the Australian Medical Association (AMA) calling for one as part of a positioning paper on the country's nutrition.

TL;DR: The AMA wants the Government to use tax policy to force up the prices of sugar-sweetened drinks to change behaviour — to make us drink them less, or even, not at all.

"The AMA has a policy of price differentiation making a difference to people's behaviour," Simon Tatz, the AMA's director of public health, said.

"That's what we saw with tobacco and that's why we support a sugar tax."

So, if soft drinks became so expensive we couldn't afford them and had to cut them out altogether, would there be any negative impacts on our nutrition?

"Sugar-sweetened beverages have absolutely no food value," Mr Tatz said.

"These are not products that if removed from consumption would lead to a loss of any kind of food value."

It's for this reason that debate around food regulation and public health often comes back to sugar-sweetened drinks.

For the AMA, taxing them is far from the single solution to the obesity or diabetes epidemics, but it's a good place to start.

Would it help?

The AMA doesn't have a specific sugar tax proposal but deferred to a Grattan Institute report released in late 2016 that said such a tax would raise more than $500 million a year.

(FWIW, at the time of the report, obesity was estimated to cost the country $5.3 billion annually.)

"It's a large amount of money that would come from a sugar tax that the Government would have to put back into health promotion," Mr Tatz said.

Mr Tatz said it would also send a signal that this kind of discretionary consumption needs to be addressed.

In February, researchers at the University of Melbourne found an Australian tax on foods high in sugar, salt and saturated fats would lead to longer lives and save the country billions in healthcare costs.

That modelling said a sugar tax alone would result in 1.2 additional years of healthy life per 100 Australians.

We consume more sugar-sweetened drinks than Britons, but the UK implemented a sugar tax in 2016.

Mexico did the same thing while improving water infrastructure in the country to encourage residents to drink that instead.

Social movement NCD Free publishes data on sugar taxes introduced around the world (its mission is to reduce the amount of preventable non-communicable diseases).

Should Australia introduce a sugar tax, it would join 28 other countries and seven US cities in doing so.

The global social movement NCD Free has launched an infographic detailing sugar taxes that have been implemented around the world. ( Twitter: @NCDFREE )

Two years after Mexico introduced the tax, NCD Free reports "sugary drink purchases decreased by 7.6 per cent" and over 10 years this "will prevent up to 134,000 cases of diabetes".

Mr Tatz:

American and England are moving much more quickly than Australia because they realised the cost of diabetes and obesity is much higher than a tax.

Will it happen here?

Well, we've been down this road before and the answer is still probably not.

When the UK sugar-sweetened tax was introduced, public health groups warned Australia needed to follow suit. Our mate Jamie Oliver even sent an anything-but-subtle message to get it done.

But the Federal Government says it won't happen on its watch.

On Sunday, a spokesperson for federal Health Minister Greg Hunt said in a statement:

"Obesity and poor diets are complex public health issue with multiple contributing factors, requiring a community-wide approach as well as behaviour change by individuals. "We do not support a new tax on sugar to address this issue. "Fresh fruit and vegetables are already effectively discounted as they do not have a GST applied."

The comments are in line with those of Coalition backbencher George Christensen who spoke to the New York Times recently.

The Times travelled to Mackay, a sugar cane town in Mr Christensen's electorate, and asked: "Does Australia need a sugar intervention?"

Mr Christensen told The Times:

"Make no bones about it, I'm opposed to a sugar tax because I think it demonises a product that is a lynchpin of this area that I live in."

Labor's position is similar.

"We don't have a plan for a sugar tax at the moment," deputy Opposition leader Tanya Plibersek said.

Instead, Labor supports "food reformulation" (the reduction of sugar, salt and calories in food) and working with health professionals on a "strong prevention strategy", she said.

It's not just about the sugar in soft drink

For the AMA — as well as Choice and the Obesity Coalition — it's about a lot more than soft drink.

They want labels changed to make it a lot easier to know whether you're eating added sugars or those that occur naturally in the food product's ingredients.

Because, sugar ain't sugar.

Sucrose is very different to lactose and your body treats it as such, but on a standard food label both would be lumped into one sugar item on the nutritional panel.

We found this example of a block of chocolate that broke it down further:

A food label on a block of chocolate displays the different types of sugar in the product. ( ABC News: Emily Clark )

The AMA wants front-of-pack labelling to address sugar, particularly the Health Star Rating (HSR) system.

"The AMA believes that the HSR should be adapted to help people to distinguish between added and naturally-occurring sugars in processed foods," the position statement reads.

The Health Star Rating System makes has promotional material that says "the more stars, the healthier". ( healthstarrating.gov.au )

The HSR has been criticised in the past for being too simplistic and not appropriately evaluating sugar.

The AMA has also recommended: