Science Party is all about evidence-based policy. Today the Greens suggested that Australia put a 20% tax on sugar. There's only one problem: we know it won't work. 

When the GST was introduced, it put a 10% tax on non-fresh food: effectively a tax on unhealthy food and beverages. We've had a fat/sugar tax since 1999, and what has happened? Australia got more overweight and had more diabetes. 

Here's us getting more diabetes:

Source: AIHW

And here's us getting more overweight:

Source: ABS

Taxes on the consumption of sugars and fats, as we've had for the last 17 years, are not going to reduce diabetes or obesity.

EDIT:
To reinforce the sentence above, some issues were raised on Facebook. In particular, there may be small marginal changes in behaviour that the GST caused, with which I agree. The core point of this article is that the GST did NOT arrest the increase in diabetes and obesity. That is, small changes in the price of goods will not stop people eating these products. There are much more important issues at play.