The Greens would support an investigation into how a 'fat tax' on processed food in New Zealand's supermarkets could be imposed.
But the government has dismissed the idea, saying it would add to the burden of families in tight economic times.
Economist Gareth Morgan is calling for the move in his new book, Appetite for Destruction, which says unhealthy processed foods should be taxed at a higher rate than healthier options as a way to combat the country's obesity epidemic.
He told TVNZ's Q+A programme fast food was only one factor of the problem, but the main focus needed to be on processed foods sold in supermarkets.
"You go through a supermarket and it's virtually all now processed food, which is not a crime in its own right, obviously, but when you do the decomposition of processed food and you see how energy intensive it is and how nutrient light it is, our bodies simply can't handle it."